Add README link to run Example Notebooks in MyBinder (#496)

* Add link to run Example Notebooks in MyBinder

The MyBinder website provides free, cloud-based hosting of jupyter notebooks, built from public git repos!! :)

I was able to just enter this repo's URL into the builder on https://mybinder.org/, and it correctly set up the repo based on the Dockerfile and everything seems to work! :) This means with one-click, people can open a browser-based environment and start interacting with the tutorial! :)

* Oops, fix typo in README.rst

README.rst

@@ -22,6 +22,12 @@ Hamiltonians. For more information, see our
 
 .. image:: https://img.shields.io/badge/python-2.7%2C%203.4%2C%203.5%2C%203.6-brightgreen.svg
 
+
+Run the interactive Jupyter Notebooks on MyBinder:
+
+.. image:: https://mybinder.org/badge_logo.svg
+    :target: https://mybinder.org/v2/gh/quantumlib/OpenFermion/master?filepath=examples
+
 Plugins
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