Add binder link

Author: mandli

README.md

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 Jupyter notebooks and other materials developed for the Columbia course APMA 4300
 
 <a rel="license" href="http://creativecommons.org/licenses/by/4.0/"><img alt="Creative Commons License" style="border-width:0" src="https://i.creativecommons.org/l/by/4.0/88x31.png" /></a><br />This work is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution 4.0 International License</a>.
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+[![Binder](http://mybinder.org/badge.svg)](http://mybinder.org:/repo/mandli/intro-numerical-methods)