add keybase documentation

Gateway-config-(channel-rules).md

@@ -38,6 +38,10 @@ Below you can find how the channels (`protocolchannel` and `protocol2channel`) s
 - rocketchat
   - `#channel_name`
     - \# is required (also for private channels)
+- keybase
+  - `channel_name`
+    - without the #
+    - if your team doesn't have multiple channels, use `general`
 - matrix
   - `#channel:server`
     - e.g. `#yourchannel:matrix.org`