updated README

Author: sommersoft

README.rst

@@ -30,15 +30,7 @@ This is easily achieved by downloading
 Usage Example
 =============
 
-See examples/simpletest.py for a demo of the usage.
-
-API Reference
-=============
-
-.. toctree::
-   :maxdepth: 2
-
-   api
+See examples/tsl2591_simpletest.py for a demo of the usage.
 
 Contributing
 ============
@@ -70,3 +62,27 @@ Then run the build:
 .. code-block:: shell
 
     circuitpython-build-bundles --filename_prefix adafruit-circuitpython-tsl2591 --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):
+
+.. code-block:: shell
+
+    python3 -m venv .env
+    source .env/bin/activate
+    pip install Sphinx sphinx-rtd-theme
+
+Now, once you have the virtual environment activated:
+
+.. code-block:: shell
+
+    cd docs
+    sphinx-build -E -W -b html . _build/html
+
+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.
+