Fix README.chromium for llvm Bug:b/442971025 Change-Id: I772ce7559c76c5586a6ffd51e03d402e9d4bb47c Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6914255 Reviewed-by: Charlie Lao <cclao@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Auto-Submit: Jordan Brown <rop@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>