First pass at commands narrative documentation.

discord/ext/commands/bot.py

@@ -276,7 +276,7 @@ class BotBase(GroupMixin):
             The function that was used as a global check.
         call_once: bool
             If the function should only be called once per
-            :meth:`.invoke` call.
+            :meth:`.Command.invoke` call.
         """
 
         if call_once:
@@ -308,7 +308,7 @@ class BotBase(GroupMixin):
         """A decorator that adds a "call once" global check to the bot.
 
         Unlike regular global checks, this one is called only once
-        per :meth:`.invoke` call.
+        per :meth:`.Command.invoke` call.
 
         Regular global checks are called whenever a command is called
         or :meth:`.Command.can_run` is called. This type of check