Update irker documentation to mention an irker bug with key-protected channels.

Signed-off-by: Mattia Rizzolo <mattia@debian.org>

doc/user/project/integrations/irker.md

@@ -47,4 +47,8 @@ Irker accepts channel names of the form `chan` and `#chan`, both for the
 case, `Aorimn` is treated as a nick and no more as a channel name.
 
 Irker can also join password-protected channels. Users need to append
-`?key=thesecretpassword` to the chan name.
+`?key=thesecretpassword` to the chan name.  When using this feature remember to
+**not** put the `#` sign in front of the channel name; failing to do so will
+result on irker joining a channel literally named `#chan?key=password` henceforth
+leaking the channel key through the `/whois` IRC command (depending on IRC server
+configuration). This is due to a long standing irker bug.