Add a note to irc2sql about using rpc_data instead.

data/anope.example.conf

@@ -1403,10 +1403,17 @@ include
 }
 
 /*
- * IRC2SQL Gateway
+ * [DEPRECATED] IRC2SQL Gateway
+ *
  * This module collects data about users, channels and servers. It doesn't build stats
  * itself, however, it gives you the database, it's up to you how you use it.
  *
+ * This module is deprecated in favour of the RPC interface and the rpc_data
+ * module. This should provide almost all of the same information as irc2sql but
+ * without requiring MySQL and with much better performance. If you have a use
+ * case which is not covered by rpc_data then please open an issue so we can
+ * extend rpc_data before irc2sql is removed.
+ *
  * Requires a MySQL Database and MySQL version 5.5 or higher
  */
 #include