Update docs for auth.getUser() to add reference to auth.getSession() as a faster alternative

spec/supabase_js_v2.yml

@@ -356,6 +356,7 @@ functions:
     notes: |
       - This method gets the user object from the current session.
       - Fetches the user object from the database instead of local session.
+      - Should be used only when you require the most current user data. For faster results, `getSession().session.user` is recommended.
     examples:
       - id: get-the-logged-in-user-with-the-current-existing-session
         name: Get the logged in user with the current existing session