Update readme with how to run regression testing script Updates CaptureAndReplay.md with how to run capture_replay_tests.py. Explains certain important flags and their effects on the behavior of the script. Bug: angleproject:4817 Change-Id: I628edf57cde51d2a6f667fbfd7dc937964badbac Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2336188 Commit-Queue: Manh Nguyen <nguyenmh@google.com> Reviewed-by: Cody Northrop <cnorthrop@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>