Add Metal progress to README
Add Metal progress to README

Just to let users of ANGLE aware of

Bug: angleproject:2634
Change-Id: I241ed569a967e8c427cb5cc2e6d82c73c17e320c
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1906621
Commit-Queue: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>
Reviewed-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>

ppy/angle,ppy/angle,ppy/angle,ppy/angle