Add missing pins.rst
Add missing pins.rst

- Got left out of the commit which added analog, gpio, and pwm docs!

Change-Id: Id87ad3601233ee99e793476084fd160d3d56df22
GitOrigin-RevId: 16ccf4e7b87c10077045921d5040a322aab0dd4c

google-coral/coralmicro,google-coral/coralmicro,google-coral/coralmicro,google-coral/coralmicro,google-coral/coralmicro