Add index for notebooks, until nbviewer can do it for us automatically.

examples/notebooks/README.md

@@ -0,0 +1,6 b''
+# Notebook examples
+
+*
+  [Simple animations Using clear_output](http://nbviewer.ipython.org/urls/raw.github.com/ipython/ipython/master/examples/notebooks/Animations%2520Using%2520clear_output.ipynb).
+  
+