Added PyPi installation instructions

Author: evaherrada

README.rst

@@ -40,7 +40,7 @@ This is easily achieved by downloading
 `a library and driver bundle <https://github.com/adafruit/Adafruit_CircuitPython_Bundle>`_.
 
 Installing from PyPI
---------------------
+====================
 On supported GNU/Linux systems like the Raspberry Pi, you can install the driver locally `from
 PyPI <https://pypi.org/project/adafruit-circuitpython-pcf8523/>`_. To install for current user: