Document the JID escaping with xep 106

doc/biboumi.1.rst

@@ -229,6 +229,12 @@ not allowed in the local part of a JID (for example '@').  If you need to send a
 message to a nick containing such a character, you can use a jid like
 ``%irc.example.com@biboumi.example.com/AnnoyingNickn@me``, because the JID
 ``AnnoyingNickn@me%irc.example.com@biboumi.example.com`` would not work.
+And if you need to address a channel that contains such invalid characters, you
+have to use `jid-escaping <http://www.xmpp.org/extensions/xep-0106.html#escaping>`,
+and replace each of these characters with their escaped version, for example to
+join the channel ``#b@byfoot``, you need to use the following JID:
+``#b\40byfoot%irc.example.com@biboumi.example.com``.
+
 
 Examples: