update requirements in readme

README.md

 # VirtFlow_GUI
 
-To use just start  **GUI_Elbow.py** in a python3 environment. Necessary packages: Numpy, Scipy, json
+To use just start  **GUI_Elbow.py** in a python3 environment. 
+Required python packages: Numpy, Scipy, json, wx, matplotlib
 
 ## Functionality