Add `betas.md` (#22734)

docs/betas.md

@@ -0,0 +1,29 @@
+# Beta features
+
+Beta features are features that are not ready for production yet but the team
+wants more people to try the features and give feedback on them.
+
+Before a feature gets into its beta phase, it is often a labs feature (see
+[Labs](https://github.com/matrix-org/matrix-react-sdk/blob/develop/docs/labs.md)).
+
+**Be warned! Beta features may not be completely finalised or stable!**
+
+## Threaded Messaging (`feature_thread`)
+
+Threading allows users to branch out a new conversation from the main timeline
+of a room. This is particularly useful in high traffic rooms where multiple
+conversations can happen in parallel or when a single discussion might stretch
+over a very long period of time.
+
+Threads can be access by clicking their summary below the root event on the room
+timeline. Users can find a comprehensive list of threads by click the icon on
+the room header button.
+
+This feature might work in degraded mode if the homeserver a user is connected
+to does not advertise support for the unstable feature `org.matrix.msc3440` when
+calling the `/versions` API endpoint.
+
+## Video rooms (`feature_video_rooms`)
+
+Enables support for creating and joining video rooms, which are persistent video
+chats that users can jump in and out of.

docs/labs.md

@@ -4,6 +4,9 @@ If Labs is enabled in the [Element config](config.md), you can enable some of th
 to `Settings->Labs`. This list is non-exhaustive and subject to change, chat in
 [#element-web:matrix.org](https://matrix.to/#/#element-web:matrix.org) for more information.
 
+If a labs features gets more stable, it _may_ be promoted to a beta feature
+(see [Betas](https://github.com/matrix-org/matrix-react-sdk/blob/develop/docs/betas.md)).
+
 **Be warned! Labs features are not finalised, they may be fragile, they may change, they may be
 dropped. Ask in the room if you are unclear about any details here.**