readme: adding a TOC
+***
PEX
-===
+***
.. image:: https://travis-ci.org/pantsbuild/pex.svg?branch=master
:target: https://travis-ci.org/pantsbuild/pex
.. image:: https://img.shields.io/pypi/l/pex.svg
@@ -11,6 +12,10 @@ PEX
.. image:: https://img.shields.io/pypi/wheel/pex.svg
:target: https://pypi.org/project/pex/#files
+.. contents:: **Contents**
+
+Overview
+========
pex is a library for generating .pex (Python EXecutable) files which are
executable Python environments in the spirit of `virtualenvs <http://virtualenv.org>`_.
pex is an expansion upon the ideas outlined in
