Add notes warning that fetch_ methods are api calls

Also recommends using cache attributes/methods instead

discord/client.py

@@ -861,6 +861,10 @@ class Client:
             Using this, you will only receive :attr:`Guild.owner`, :attr:`Guild.icon`,
             :attr:`Guild.id`, and :attr:`Guild.name` per :class:`Guild`.
 
+        .. note::
+
+            This method is an API call. For general usage, consider :attr:`guilds` instead.
+
         All parameters are optional.
 
         Parameters
@@ -912,6 +916,10 @@ class Client:
             Using this, you will not receive :attr:`Guild.channels`, :class:`Guild.members`,
             :attr:`Member.activity` and :attr:`Member.voice` per :class:`Member`.
 
+        .. note::
+
+            This method is an API call. For general usage, consider :meth:`get_guild` instead.
+
         Parameters
         -----------
         guild_id: :class:`int`
@@ -1099,6 +1107,10 @@ class Client:
         with the user to get this information, however many operations
         do require that you do.
 
+        .. note::
+
+            This method is an API call. For general usage, consider :meth:`get_user` instead.
+
         Parameters
         -----------
         user_id: :class:`int`