Merge pull request #3 from Carreau/add-binder

Add link to run on MyBinder.org to run jupyter notebook for Free.

README.md

@@ -6,6 +6,8 @@ This project contains **pytudes**—Python programs for perfecting programmi
 
 Some are in Jupyter (IPython) notebooks, some in *.py files.
 
+[![Binder](https://mybinder.org/badge.svg)](https://mybinder.org/v2/gh/norvig/pytudes/master)
+ 
 # pytudes: Index of Jupyter (IPython) Notebooks
 
 |Logic and Number Puzzles|

requirements.txt

@@ -0,0 +1 @@
+numpy