Update the README to reflect repository contents
Update the README to reflect repository contents

Include a note about how this differs from upstream Skia and the
procedure for moving to a newer upstream branch point.

larsbergstrom/skia,akiss77/skia,vvuk/skia,nox/skia,nox/skia,akiss77/skia,nox/skia,nox/skia,mmatyas/skia,vvuk/skia,akiss77/skia,larsbergstrom/skia,mmatyas/skia,akiss77/skia,larsbergstrom/skia,mmatyas/skia,mmatyas/skia,vvuk/skia,akiss77/skia,larsbergstrom/skia,larsbergstrom/skia,larsbergstrom/skia,nox/skia,vvuk/skia,nox/skia,vvuk/skia,vvuk/skia,akiss77/skia,nox/skia,mmatyas/skia,mmatyas/skia,mmatyas/skia,nox/skia,mmatyas/skia,mmatyas/skia,vvuk/skia,akiss77/skia,akiss77/skia,vvuk/skia,larsbergstrom/skia,akiss77/skia,larsbergstrom/skia,larsbergstrom/skia,vvuk/skia,nox/skia