add pypi instructions to README.rst

Also some minor whitespace tweaks.

README.rst

@@ -15,8 +15,9 @@ Introduction
 
 Driver for the AS726x spectral sensors
 
-Dependencies
-=============
+Installation and Dependencies
+=============================
+
 This driver depends on:
 
 * `Adafruit CircuitPython <https://github.com/adafruit/circuitpython>`_
@@ -27,6 +28,26 @@ 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>`_.
 
+Installing from PyPI
+--------------------
+
+On the Raspberry Pi and other Linux systems, you can install the driver locally
+`from PyPI <https://pypi.org/project/adafruit-circuitpython-as726x/>`_.  To
+install system-wide, use:
+
+.. code-block:: shell
+
+    sudo pip3 install adafruit-circuitpython-as726x
+
+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-as726x
+
 Contributing
 ============
 
@@ -34,7 +55,7 @@ Contributions are welcome! Please read our `Code of Conduct
 <https://github.com/adafruit/adafruit_CircuitPython_AS726x/blob/master/CODE_OF_CONDUCT.md>`_
 before contributing to help this project stay welcoming.
 
-Building locally
+Building Locally
 ================
 
 Zip release files
@@ -61,8 +82,8 @@ Then run the build:
 
     circuitpython-build-bundles --filename_prefix adafruit-circuitpython-as726x --library_location .
 
-Sphinx documentation
------------------------
+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):