Merge pull request #9 from adafruit/pypi-readme-update

PyPI installation added to README

Author: brennen

README.rst

@@ -19,8 +19,8 @@ and ambient light color over I2C. Its available on
 `Adafruit as a breakout <https://www.adafruit.com/product/3595>`_.
 
 
-Dependencies
-=============
+Installation and Dependencies
+=============================
 This driver depends on:
 
 * `Adafruit CircuitPython <https://github.com/adafruit/circuitpython>`_
@@ -29,6 +29,30 @@ 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 supported GNU/Linux systems like the Raspberry Pi, you can install the driver locally `from PyPI <https://pypi.org/project/adafruit-circuitpython-apds9960/>`_. To install for current user:
+
+.. code-block:: shell
+
+    pip3 install adafruit-circuitpython-apds9960
+
+To install system-wide (this may be required in some cases):
+
+.. code-block:: shell
+
+    sudo pip3 install adafruit-circuitpython-apds9960
+
+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-apds9960
+
 Usage Example
 =============
 
@@ -168,4 +192,4 @@ Now, once you have the virtual environment activated:
 
 This will output the documentation to ``docs/_build/html``. Open the index.html in your browser to
 view them. It will also (due to -W) error out on any warning like Travis will. This is a good way to
-locally verify it will pass.
+locally verify it will pass.