Merge branch 'zj-link-broadcast-api-docs' into 'master'

Add link to broadcast messages docs

[ci skip]

See merge request !6495

doc/api/README.md

@@ -10,6 +10,7 @@ following locations:
 - [Award Emoji](award_emoji.md)
 - [Branches](branches.md)
+- [Broadcast Messages](broadcast_messages.md)
 - [Builds](builds.md)
 - [Build Triggers](build_triggers.md)
 - [Build Variables](build_variables.md)