Introduce WebRTC documentation structure and how-to

Bug: webrtc:12545
Change-Id: Iefe6f27e29885ae6825c4120eecd2c2ed4f600b2
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/211247
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33444}

g3doc/how_to_write_documentation.md

@@ -0,0 +1,63 @@
+# How to write WebRTC documentation
+
+<?% config.freshness.owner = 'titovartem' %?>
+<?% config.freshness.reviewed = '2021-03-01' %?>
+
+## Audience
+
+Engineers and tech writers who wants to contribute to WebRTC documentation
+
+## Conceptual documentation
+
+Conceptual documentation provides overview of APIs or systems. Examples can
+be threading model of a particular module or data life cycle. Conceptual
+documentation can skip some edge cases in favor of clarity. The main point
+is to impart understanding.
+
+Conceptual documentation often cannot be embedded directly within the source
+code because it usually describes multiple APIs and entites, so the only
+logical place to document such complex behavior is through a separate
+conceptual document.
+
+A concept document needs to be useful to both experts and novices. Moreover,
+it needs to emphasize clarity, so it often needs to sacrifice completeness
+and sometimes strict accuracy. That's not to say a conceptual document should
+intentionally be inaccurate. It just means that is should focus more on common
+usage and leave rare ones or side effects for class/function level comments.
+
+In the WebRTC repo, conceptual documentation is located in `g3doc` subfolders
+of related components. To add a new document for the component `Foo` find a
+`g3doc` subfolder for this component and create a `.md` file there with
+desired documentation. If there is no `g3doc` subfolder, create a new one
+and add `g3doc.lua` file there with following content:
+
+```
+config = require('/g3doc/g3doc.lua')
+return config
+```
+
+If you are a Googler also please specify an owner, who will be responsible for
+keeping this documentation updated, by adding the next lines at the beginning
+of your `.md` file immediately after page title:
+
+```
+<?\% config.freshness.owner = '<user name>' %?>
+<?\% config.freshness.reviewed = '<last review date in format yyyy-mm-dd>' %?>
+```
+
+After the document is ready you should add it into `/g3doc/sitemap.md`, so it
+will be visible for others.
+
+### Documentation format
+
+The documentation is written in g3doc, which is a markup format derived from
+markdown. This is processed by multiple tools, so we recommend using only simple
+markup, and previewing the documents in multiple viewers if possible.
+
+## Class/function level comments
+
+Documentation of specific classes and function APIs and their usage, inculding
+their purpose, is embedded in the .h files defining that API. See
+[C++ style guide](https://chromium.googlesource.com/chromium/src/+/master/styleguide/c++/c++.md)
+for pointers on how to write API documentatin in .h files.
+

g3doc/sitemap.md

@@ -1,6 +1,23 @@
+[Home](/g3doc/index.md)
+*   How to contribute
+    *   Code
+    *   [Documentation](/g3doc/how_to_write_documentation.md)
+*   Public C++ API
+*   Implementation
+    *   Network
+    *   Congestion control and bandwidth estimation
+    *   Audio
+    *   Video
+    *   DataChannel
+    *   PeerConnection
+    *   Desktop capture
+    *   Stats
 *   Testing
     *   Media Quality and performance
         *   PeerConnection Framework
             *   [Video analyzer](/test/pc/e2e/g3doc/default_video_quality_analyzer.md)
+        *   Call framework
+        *   Video codecs test framework
     *   Network emulation
         *   [Implementation](/test/network/g3doc/index.md)
+    * Performance stats collection