Move interact docs to front of widgets as a simple usecase

Author: jasongrout

docs/source/index.rst

@@ -103,8 +103,8 @@ some custom widget packages built on top of the Jupyter Widgets framework.
     examples/Widget Styling.ipynb
     examples/Widget Layout.ipynb
     examples/Layout Templates.ipynb
-    examples/Widget Custom.ipynb
     examples/Using Interact.ipynb
+    examples/Widget Custom.ipynb
     examples/Widget Low Level.ipynb
     examples/Widget Asynchronous.ipynb
     embedding.md