Add link to SDK manager to README
Add link to SDK manager to README

WonderCsabo/deckard-gradle,403462630/deckard-gradle-test,seadowg/deckard-gradle,robolectric/deckard,sweetleon/android-sample-todo-list,Mounika-Chirukuri/deckard,vogellacompany/deckard-gradle,0359xiaodong/deckard,yjliugit/gradletest