Update README.md

omemo/README.md

@@ -57,6 +57,13 @@ you have to trust at least **one** fingerprint to send messages.
 you can receive messages from fingerprints where you didnt made a trust decision, but you cant
 receive Messages from *not trusted* fingerprints
 
+## Groupchat
+
+Groupchat works only in rooms that are
+- non-anonymous
+- members-only
+- works only with contacts that you have in your roster
+
 ## Filetransfer
 
 For Filetransfer use the **httpupload** plugin.