README.md: Add Status, Contributing sections

README.md

@@ -1,6 +1,32 @@
 # ruma-client
 
-**ruma-client** is a [Matrix](https://matrix.org/) client library for [Rust](https://www.rust-lang.org/).
+**ruma-client** is a [Matrix][] client library for [Rust][].
+
+[Matrix]: https://matrix.org/
+[Rust]: https://www.rust-lang.org/
+
+## Status
+
+This project is a work in progress and not ready for production usage yet. Most endpoints that are
+available in this crate are usable with an up-to-date synapse server, but no comprehensive testing
+has been done so far.
+
+As long as the matrix client-server API is still at version 0.x, only the latest API revision is
+considered supported. However, due to the low amount of available manpower, it can take a long time
+for all changes from a new API revision to arrive in ruma-client (at the time of writing only few
+endpoints have received an update for r0.4.0).
+
+## Contributing
+
+If you want to help out, have a look at the issues here and on the other [ruma-\*][gh-org]
+repositories (ruma-client-api and ruma-events in particular contain much of the code that powers
+ruma-client).
+
+There is also a [room for ruma on matrix.org][#ruma:matrix.org], which can be used for questions
+and discussion related to any of the crates in this project.
+
+[gh-org]: https://github.com/ruma
+[#ruma:matrix.org]: https://matrix.to/#/#ruma:matrix.org
 
 ## License