adds run instructions

Author: sdaitzman

README.md

@@ -1,3 +1,5 @@
 # Daily Data Structures // Algorithms
 
-Problems via [https://www.dailycodingproblem.com/](https://www.dailycodingproblem.com/).
+Problems via [https://www.dailycodingproblem.com/](https://www.dailycodingproblem.com/).
+
+Mostly written in Python, with pytest. To run the tests, just do `$ pytest 1.py` or `$ pytest 2.py` and so on.