Update README.md

Author: cybergalactic

README.md

@@ -39,6 +39,7 @@ In order to run the main program ```main.py``` the following modules must be ins
 
  numpy https://numpy.org/install/
  matplotlib https://matplotlib.org/stable/users/installing.html
+ pytest https://docs.pytest.org
 
 The Python packages are automatically installed by uisng the command