[ADD] project: How to forecast tasks?

https://docs.google.com/document/d/1YGWI_JcoFg4HgHTwSlLsg3RjSg9wig43G-KxAH6PTFU/edit#heading=h.mzfmgxhsof20

project/planning.rst

@@ -6,3 +6,4 @@ Planning your project
    :titlesonly:
 
    planning/assignments
+   planning/forecast

project/planning/forecast.rst

@@ -1,3 +1,202 @@
 ======================
 How to forecast tasks?
-======================
+======================
+
+Introduction to forecast 
+========================
+
+Scheduling and forecasting tasks is another way to manage projects. In
+Odoo, the Forecast option gives you access to the Gantt chart.
+
+So far, you've been working with the Kanban view, which shows you the
+progress of a project and its related tasks.
+
+Now, with the Forecast option, the Gantt view gives you the big picture.
+It's highly visual which is a real plus for complex projects, and it
+helps team members to collaborate better.
+
+This option is a real benefit in terms of planning and organizing the
+workload and human resources.
+
+How to configure the projects? 
+==============================
+
+Configure the project application
+---------------------------------
+
+The **Forecast** option helps you to organize your projects. This is perfect
+when you need to set up a project with a specific deadline. Therefore,
+each task is assigned a specific timeframe (amount of hours) in which
+your employee should complete it!
+
+First you need to activate the **Forecast** option for the whole project
+application:
+
+Go to :menuselection:`Project --> Configuration --> Settings`.
+Select the Forecast option and click **Apply**.
+
+.. image:: media/forecast01.png
+    :align: center
+
+Once this is done, you still need to activate the **Forecast** option
+specifically for your **Project** (maybe you don't need the Gantt chart for
+all the projects that you manage).
+
+Configure a specific project. 
+-----------------------------
+
+When creating a new project, make sure to select the option "Allow
+Forecast" in your project settings.
+
+You'll see the **Forecast** option appearing in the top menu.
+
+.. image:: media/forecast02.png
+    :align: center
+
+If you add the Forecasting option to an existing project, whether there
+are task deadlines or not scheduled, the task won't be displayed.
+
+The tasks of a project are not related to a forecast.
+
+How to create a forecast?
+-------------------------
+
+Before creating a project with forecast, list all the tasks with the
+projected time they should take. It will help you to coordinate the
+work.
+
+In order to display the projects in the Gantt chart, you need to create
+the forecast from the task page. To create a forecast, click on the top
+left corner of the task, **Create a Forecast**.
+
+.. image:: media/forecast03.png
+    :align: center
+
+.. tip::
+    You can also create a new Forecast easily by directly clicking on an empty 
+    space in the Gantt chart calendar.
+
+The Forecast interface will fill in the name of the Project and the task
+automatically. You just need to add the dates and the time the task
+should take.
+
+.. image:: media/forecast04.png
+    :align: center
+
+.. tip::
+    The "Effective hours" field appears only if you have the **Timesheet** app 
+    installed on your database. This option helps you to see the progress of a 
+    task thanks to the integration with Timesheet.
+
+    For example: When a user fills in a Timesheet with your Project name 
+    (Analytic account), with 10 hours spent, the forecast will display 10 hours 
+    in the Estimated Time field.
+
+What are the difference between the views?
+==========================================
+
+In the **Project** app menu you have a **Forecast** menu. This sub-menu helps
+you to see the Gantt chart from different points of view: by users or by
+projects.
+
+By users : people management
+----------------------------
+
+This option displays the Gantt chart with the people assigned. Odoo's
+Gantt chart shows you who's involved; it gives you the big picture of
+the project. It's very useful to allocate your resources effectively.
+
+On the left side, first level, you can see which users are involved.
+Then, on the second level you see which projects they are assigned to.
+On the third, you see which tasks they're on.
+
+Each task is represented by a coloured rectangle. This rectangle
+reflects the duration of the task in the calendar.
+
+The top rectangle on the first level is the sum of all the tasks
+compiled from the third level. If it's green, it means that the total
+time allocated to that user is less than 100%. When it's red, it means
+that this user is assigned to multiple tasks which total more than 100%
+of his/her time.
+
+.. image:: media/forecast05.png
+    :align: center
+
+Plan the workload
+~~~~~~~~~~~~~~~~~
+
+When creating a forecast, you have to select the time the user should
+spend on it. 100% means that your user should work on it full time
+during those days. He/She has no other tasks to work on. So you can
+decide from 1 to 100% how your users should organize their time between
+different tasks.
+
+The power of integration helps you to avoid double booking an employee.
+For example, if your expert is already at 40% on another task in another
+project, you can book him/her for only 60% for that period.
+
+In the example below, the user "Administrator" is working on 2 projects
+("IT1367 Delivery Phases" and "Implementation Process56"). The user is
+assigned to both projects with a total of 110% of their time. This is
+too much so the Project Manager should change the users assigned to the
+task. Otherwise, the PM can change the dedicated time or the dates, to
+make sure that this is feasible.
+
+.. image:: media/forecast06.png
+    :align: center
+
+Gantt view advantages
+~~~~~~~~~~~~~~~~~~~~~
+
+This Gantt view ‘by user' helps you to better plan your human resources.
+You avoid confusion about the the tasks and the assignations of the
+users. The Gantt Chart is highly visual and helps to comprehend all the
+different elements at once. Also, you immediately know what has to be
+done next. This method helps you to better understand the relations
+between the tasks.
+
+The dynamic view of the Gantt in Odoo allows you to:
+
+-   change the time and date of a forecast by clicking and sliding the
+    tasks in the future or in the past
+
+-   create a new forecast into the Gantt chart immediately
+
+-   modify an existing forecast
+
+-   change the length of a task by extending or shortening the rectangle.
+
+By projects: project management
+-------------------------------
+
+The Gantt Chart is the perfect view of a project to better understand
+the interactions between the tasks. You can avoid overlapping tasks or
+starting one too early if another one isn't finished. Odoo Gantt chart
+is clear and helps you to coordinate tasks efficiently.
+
+This option displays the Gantt chart by showing the projects on the
+first level of hierarchy.
+
+On the left side, first level, you can see the projects. Then, on the
+second level you see which users are assigned. On the third, you see
+which tasks they're on.
+
+This view won't show your HR time. The colours don't apply. (see **By
+Users** section)
+
+.. image:: media/forecast07.png
+    :align: center
+
+Gantt view advantages
+~~~~~~~~~~~~~~~~~~~~~
+
+The dynamic view of the Gantt in Odoo allows you to:
+
+-   change the time and date of a forecast by clicking and sliding the
+    tasks in the future or in the past
+
+-   create a new forecast into the Gantt chart immediately
+
+-   modify an existing forecast
+
+-   change the length of a task by extending or shortening the rectangle.