add snomask documentation

docs/MANUAL.md

@@ -503,9 +503,9 @@ To unset this mode and let anyone speak to you:
 
     /mode dan -R
 
-### +s - Server Notice Masks
+### +s - Server Notice Masks ("snomasks")
 
-This is a special 'list mode'. If you're an IRC operator, this mode lets you see special server notices that get sent out. See the Server Notice Masks section for more information on this mode.
+This is a special 'list mode'. If you're an IRC operator, this mode lets you see special server notices that get sent out. See `/helpop snomasks` (as an operator) for more information on this mode.
 
 ### +Z - TLS
 

irc/help.go

@@ -83,6 +83,7 @@ Oragono supports the following server notice masks for operators:
   t  |  Local /STATS usage.
   u  |  Local client account actions.
   x  |  Local X-lines (DLINE/KLINE/etc).
+  v  |  Local vhost changes.
 
 To set a snomask, do this with your nickname: