Merge pull request #1 from dannystaple/docs-update

Add a link to the related rp2pio docs

Author: dannystaple

docs/index.rst

@@ -38,6 +38,7 @@ Table of Contents
 
     Download <https://github.com/adafruit/Adafruit_CircuitPython_PIOASM/releases/latest>
     CircuitPython Reference Documentation <https://circuitpython.readthedocs.io>
+    CircuitPython rp2pio Reference Documentation <https://circuitpython.readthedocs.io/en/latest/shared-bindings/rp2pio>
     CircuitPython Support Forum <https://forums.adafruit.com/viewforum.php?f=60>
     Discord Chat <https://adafru.it/discord>
     Adafruit Learning System <https://learn.adafruit.com>