Update README.md

Author: NishkarshRaj

README.md

@@ -2,6 +2,12 @@
 
 Use GitHub Actions to complile C/C++ source codes to generate OpenGL output.
 
+## How to use:
+
+1. Add a .cpp/.c source file in action-a/ folder.
+2. Add the file name in both Dockerfile and script file replacing the default src.cpp file
+3. push to the master branch to run the action
+
 ## How to contribute
 
 This project is open sourced and contributions in all forms are welcomed.