add docs link to readme

Author: FoamyGuy

README.rst

@@ -100,6 +100,11 @@ Usage Example
 More examples and details can be found in the `adafruit_framebuf docs <https://circuitpython.readthedocs.io/projects/framebuf/en/latest>`__.
 
 
+Documentation
+=============
+
+API documentation for this library can be found on `Read the Docs <https://circuitpython.readthedocs.io/projects/ssd1306/en/latest/>`_.
+
 Contributing
 ============