Add shadowircd5 section to doc/IRCD.

A copy of the charybdis section, except the part about TS5
(no version of shadowircd5 supports TS5 links).

doc/IRCD

@@ -225,6 +225,17 @@ as it reduces ghosts/desyncs and propagates user IP addresses. Although
 Atheme does not support IPv6 connections itself, user IPv6 addresses will
 be properly stored and logged.
 
+shadowircd5
+-----------
+
+You will need a service{} block on all servers.
+
+If you want to use akills, you need shared{} blocks for services on all servers
+on the network.
+
+Although Atheme does not support IPv6 connections itself, user IPv6 addresses
+will be properly stored and logged.
+
 ultimate3
 ---------