Improve documentation of action=parse (followup Ie4f7324c)

The documentation for action=parse needs clarification, particularly in
light of the changes made in Ie4f7324c which were too hastily merged.

Also, add the RELEASE-NOTES entry missing from Ie4f7324c.

Change-Id: Ia8847f7e99620a9f7af24956d972c882f78aae26