[DOC] add architecture notes on rendering pipeline

doc/architecture/rendering.md

@@ -0,0 +1,34 @@
+# 🦉 Rendering Pipeline 🦉
+
+We explain here how Owl is designed, from the perspective of its rendering
+pipeline.
+
+Warning: these notes are technical by nature, and intended for people working
+on Owl (or interested in understanding its design).
+
+## Overview
+
+A rendering occurs in two phases:
+
+- virtual rendering: this generates the virtual dom in memory, asynchronously
+- patch: applies a virtual tree to the screen (synchronously)
+
+
+There are several classes involved in a rendering:
+
+- components
+- a scheduler
+- fibers: small objects containing some metadata, associated with a rendering of
+  a specific component
+
+
+Components are organized in a dynamic component tree, visible in the user
+interface.  Whenever a rendering is initiated in a component `C`:
+- a fiber is created on `C` with the rendering props information
+- the virtual rendering phase starts on C (will asynchronously render all the
+  child components)
+- the fiber is added to the scheduler, which will poll continuously, every
+  animation frame, if the fiber is done
+- once it is done, the scheduler will call the task callback, which will apply
+  the patch (if it was not cancelled in the meantime).
+

doc/readme.md

@@ -62,7 +62,6 @@ Note that for convenience, the `useState` hook is also exported at the root of t
 - [Store](reference/store.md)
 - [Tags](reference/tags.md)
 - [Utils](reference/utils.md)
-- [Virtual DOM](architecture/vdom.md)
 
 ## Learning Resources
 
@@ -73,3 +72,11 @@ Note that for convenience, the `useState` hook is also exported at the root of t
 - [Comparison with React/Vue](comparison.md)
 - [Tooling](tooling.md)
 - [Templates to start Owl applications (external link)](https://github.com/ged-odoo/owl-templates)
+
+## Architecture
+
+This section explains in more detail the inner workings of Owl. It is more
+useful for people working on Owl code.
+
+- [Virtual DOM](architecture/vdom.md)
+- [Rendering](architecture/rendering.md)