Add explanation to README.md
Add explanation to README.md

SethsApps/ud867,DevDoug/AndroidNanoDegreeProjectFour,DevDoug/AndroidNanoDegreeProjectFour,Wertros/GradleTutorial,Sushant-M/Joke_Telling_App,Wertros/GradleTutorial,udacity/ud867,SethsApps/ud867,udacity/ud867,KarthicK10/AND_Project_4_BuildItBigger,Sushant-M/Joke_Telling_App,KarthicK10/AND_Project_4_BuildItBigger