Added link to sphinx section in learn guide

Author: evaherrada

README.rst

@@ -65,3 +65,5 @@ Contributing
 Contributions are welcome! Please read our `Code of Conduct
 <https://github.com/adafruit/Adafruit_CircuitPython_ESP32SPI/blob/master/CODE_OF_CONDUCT.md>`_
 before contributing to help this project stay welcoming.
+
+For information on building library documentation, please check out `this guide<https://learn.adafruit.com/creating-and-sharing-a-circuitpython-library/sharing-our-docs-on-readthedocs#sphinx-5-1>`_.