Create README.md

My first commit here titled, ".add()method 3 of 4 tests written" is intended to show all 4 of my .add()method tests failing. I had gone forward with writing the code in main.js in order to make sure the tests i had written were valid. I then deleted the main.js code, expecting all 4 tests to fail again. However, it is showing the 2nd and 3rd tests as passing now. Not sure why this is happening???