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 <geofflang@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>