add intro text to landing page

Author: willingc

docs/source/index.rst

@@ -6,6 +6,18 @@ ipywidgets
     :Release: |version|
     :Date: |today|
 
+**ipywidgets**, also known as jupyter-widgets or simply widgets, are
+`interactive HTML widgets <https://github.com/jupyter-widgets/ipywidgets/blob/master/docs/source/examples/Index.ipynb>`_
+for Jupyter notebooks and the IPython kernel.
+
+Notebooks come alive when interactive widgets are used. Users gain control of
+their data and can visualize changes in the data.
+
+Learning becomes an immersive, fun experience. Researchers can easily see
+how changing inputs to a model impact the results. We hope you will add
+ipywidgets to your notebooks, and we're here to help you get started.
+
+
 .. toctree::
     :caption: User Guide
     :maxdepth: 1