readme: add contributing instructions

README.md

@@ -5,3 +5,16 @@ A simple bot for helping post standup updates in a particular room.
 ## Usage
 
 Run `!standupbot help` for details on how to use it.
+
+## Contribute
+
+Join
+[#standupbot-dev:sumnerevans.com](https://matrix.to/#/#standupbot-dev:sumnerevans.com)
+on Matrix for general discussion about the project.
+
+Contributions are welcome! Please start discussions and send patches to the
+[~sumner/public-inbox][public-inbox] mailing list. Confirmed bugs and approved
+feature requests can be added to the [standupbot ticket tracker][tracker].
+
+[public-inbox]: https://lists.sr.ht/~sumner/public-inbox
+[tracker]: https://todo.sr.ht/~sumner/standupbot