Don't set update_interval: never along with test_card (#5154)

Author: ChadMatsalla

components/display/index.rst

@@ -629,6 +629,11 @@ To help the graphics display team determine the best way to help you, **a pictur
 Should you `create an issue <https://github.com/esphome/esphome/issues>`__ in GitHub regarding your display, please
 be sure to **include a link to where you purchased the display** so that we can validate the configuration you've used.
 
+.. note::
+
+    If you set `update_interval: never` in your config you will not see the test card because the `display:` component will not update the display with the test card. If you want to see a test card, set `update_interval:` to something other than `never`.
+
+
 .. note::
 
     For displays in 8 bit mode you will see distinct color blocks rather than a smooth gradient.