Add script to auto-generate our index of example notebooks.

It's highly hard-coded for now, but will do in the meantime.  We can
generalize it later, but we're really hurting by not having this index
anywhere.

tools/mknbindex.py

@@ -0,0 +1,36 b''
+#!/usr/bin/env python
+"""Simple script to auto-generate the index of notebooks in a given directory.
+"""
+
+import glob
+import urllib
+
+notebooks = sorted(glob.glob('*.ipynb'))
+
+tpl = ( '* [{0}](http://nbviewer.ipython.org/url/github.com/ipython/ipython/'
+        'raw/master/examples/notebooks/{1})' )
+
+idx = [ 
+"""# A collection of Notebooks for using IPython effectively
+
+The following notebooks showcase multiple aspects of IPython, from its basic
+use to more advanced scenarios.  They introduce you to the use of the Notebook
+and also cover aspects of IPython that are available in other clients, such as
+the cell magics for multi-language integration or our extended display
+protocol.
+
+For beginners, we recommend that you start with the 5-part series that
+introduces the system, and later read others as the topics interest you.
+
+Once you are familiar with the notebook system, we encourage you to visit our
+[gallery](https://github.com/ipython/ipython/wiki/A-gallery-of-interesting-IPython-Notebooks)
+where you will find many more examples that cover areas from basic Python
+programming to advanced topics in scientific computing.
+"""]
+
+idx.extend(tpl.format(nb.replace('.ipynb',''), urllib.quote(nb)) 
+           for nb in notebooks)
+
+with open('README.md', 'w') as f:
+    f.write('\n'.join(idx))
+    f.write('\n')