Add more info to the sv_lan command

Official Description for the sv_lan command:
Server is a lan server ( no heartbeat, no authentication, no non-class C addresses )

CounterStrikeGlobalOffensive/server.cfg

@@ -20,7 +20,7 @@ sv_password ""
 // Example: sv_contact "email@example.com"
 sv_contact ""
 
-// LAN mode - If set the server will not show on the internet.
+// LAN mode - Server is a LAN server; can't connect from the internet. VAC (Valve Anti-Cheat) is disabled in this mode.
 // Default: sv_lan 0
 sv_lan 0