ENH: add info about how to remove tests from stable, release branch builds.
ENH: add info about how to remove tests from stable, release branch builds.

From exchange with <kjellander@google.com>.

samdutton/webrtc-org,webrtc/webrtc-org,webrtc/webrtc-org,Scintillo/webrtc-org,louquillio/webrtc-org,Scintillo/webrtc-org,louquillio/webrtc-org,louquillio/webrtc-org,Scintillo/webrtc-org,samdutton/webrtc-org,webrtc/webrtc-org