fix documentation for GuildChannel.set_permissions

discord/abc.py

@@ -552,8 +552,9 @@ class GuildChannel:
         -----------
         target: Union[:class:`~discord.Member`, :class:`~discord.Role`]
             The member or role to overwrite permissions for.
-        overwrite: :class:`~discord.PermissionOverwrite`
+        overwrite: Optional[:class:`~discord.PermissionOverwrite`]
-            The permissions to allow and deny to the target.
+            The permissions to allow and deny to the target, or `None` to
+            delete the overwrite.
         \*\*permissions
             A keyword argument list of permissions to set for ease of use.
             Cannot be mixed with ``overwrite``.