Clarify how to reference WebRTC bugs in TODOs

Bug: None
No-Try: true
Change-Id: Iaa8b57dea096ef0588979faa5ba7c22dcff1dada
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/267282
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Emil Lundmark <lndmrk@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37387}
diff --git a/g3doc/style-guide.md b/g3doc/style-guide.md
index 421a7d9..9d713c6 100644
--- a/g3doc/style-guide.md
+++ b/g3doc/style-guide.md
@@ -62,12 +62,14 @@
 ### `TODO` comments
 
 Follow the [Google styleguide for `TODO` comments][goog-style-todo]. When
-referencing a WebRTC bug, prefer the url form, e.g.
+referencing a WebRTC bug, prefer using the URL form (excluding the scheme part):
 
 ```cpp
 // TODO(bugs.webrtc.org/12345): Delete the hack when blocking bugs are resolved.
 ```
 
+The short form used in commit messages, e.g. `webrtc:12345`, is discouraged.
+
 [goog-style-todo]: https://google.github.io/styleguide/cppguide.html#TODO_Comments
 
 ### Deprecation