Capture/Replay: Clarify that capture is disabled by default. https://crrev.com/c/3163360 disabled capture when no vars are specified by changing the ANGLE_CAPTURE_FRAME_END default from 10 to 0. Bug: angleproject:6397 Change-Id: I22efceafa412fabf283542cb05f54a84d308931d Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3503699 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Cody Northrop <cnorthrop@google.com> Auto-Submit: Roman Lavrov <romanl@google.com> Commit-Queue: Roman Lavrov <romanl@google.com>