fix branch name in conduct link

Author: FoamyGuy

README.rst

@@ -63,7 +63,7 @@ Contributing
 ============
 
 Contributions are welcome! Please read our `Code of Conduct
-<https://github.com/adafruit/Adafruit_CircuitPython_WSGI/blob/master/CODE_OF_CONDUCT.md>`_
+<https://github.com/adafruit/Adafruit_CircuitPython_WSGI/blob/main/CODE_OF_CONDUCT.md>`_
 before contributing to help this project stay welcoming.
 
 Sphinx documentation