cmd-review.txt: Add clarification in documentation of --force-message

Add a paragraph in the documentation explaining that if the review
command fails because the user is not permitted to change the label,
the --force-message option will not be effective.

Also fix a couple of minor typos.

Change-Id: I6fdcd54018203a573cd1de3f39f2904f30a0da8a
1 file changed