Add CODE_OF_CONDUCT.md
Add CODE_OF_CONDUCT.md

Change-Id: I350c6a0ffa74879f23b397ff949627b6705b4d1a

wikimedia/apps-android-wikipedia,dbrant/apps-android-wikipedia,wikimedia/apps-android-wikipedia,dbrant/apps-android-wikipedia,wikimedia/apps-android-wikipedia,dbrant/apps-android-wikipedia,dbrant/apps-android-wikipedia,dbrant/apps-android-wikipedia,wikimedia/apps-android-wikipedia