add pypi instructions to README

Author: Brennen Bearnes

README.rst

@@ -1,4 +1,3 @@
-
 Introduction
 ============
 
@@ -17,16 +16,38 @@ Introduction
 Support for the ADS1x15 series of analog-to-digital converters. Available in 12-bit (ADS1015)
 and 16-bit (ADS1115) versions.
 
-Dependencies
-=============
+Installation & Dependencies
+===========================
+
 This driver depends on:
 
 * `Adafruit CircuitPython <https://github.com/adafruit/circuitpython>`_
 * `Bus Device <https://github.com/adafruit/Adafruit_CircuitPython_BusDevice>`_
 
 Please ensure all dependencies are available on the CircuitPython filesystem.
-This is easily achieved by downloading
-`the Adafruit library and driver bundle <https://github.com/adafruit/Adafruit_CircuitPython_Bundle>`_.
+This can be most easily achieved by downloading and installing
+`the Adafruit library and driver bundle <https://github.com/adafruit/Adafruit_CircuitPython_Bundle>`_ on
+your device.
+
+Installing from PyPI
+--------------------
+
+On the Raspberry Pi, you can install the driver locally
+`from PyPI <https://pypi.org/project/adafruit-circuitpython-ads1x15/>`_.  To
+install system-wide, use:
+
+.. code-block:: shell
+
+    sudo pip3 install adafruit-circuitpython-ads1x15
+
+To install in a virtual environment in your current project:
+
+.. code-block:: shell
+
+    mkdir project-name && cd project-name
+    python3 -m venv .env
+    source .env/bin/activate
+    pip3 install adafruit-circuitpython-ads1x15
 
 Usage Example
 =============
@@ -94,7 +115,7 @@ Then run the build:
     circuitpython-build-bundles --filename_prefix adafruit-circuitpython-ads1x15 --library_location .
 
 Sphinx documentation
------------------------
+--------------------
 
 Sphinx is used to build the documentation based on rST files and comments in the code. First,
 install dependencies (feel free to reuse the virtual environment from above):