Add missing permission in clone documentation

discord/abc.py

@@ -679,6 +679,9 @@ class GuildChannel:
         Clones this channel. This creates a channel with the same properties
         as this channel.
 
+        You must have the :attr:`~discord.Permissions.manage_channels` permission to
+        do this.
+
         .. versionadded:: 1.1
 
         Parameters