add displayio to mock docs

Author: FoamyGuy

docs/conf.py

@@ -27,7 +27,7 @@
 # Uncomment the below if you use native CircuitPython modules such as
 # digitalio, micropython and busio. List the modules you use. Without it, the
 # autodoc module docs will fail to generate with a warning.
-autodoc_mock_imports = ["bitmaptools"]
+autodoc_mock_imports = ["bitmaptools", "displayio"]
 
 autodoc_preserve_defaults = True