Add chatty.js to the list.

Chatty supports matrix protocol natively when logged in.

[Chatty](https://source.puri.sm/Librem5/chatty)

Start by finding the list of Matrix clients or applications in the matrix.to repository, then compare its existing entries with the Chatty project linked in the issue. Add Chatty to the appropriate list with its Matrix support noted, and verify that the list renders correctly.

Written by the indexing model from the issue text.