The documentation for creating reviews with rbt status-update set

indicated that body_top and body_bottom content should be set inside of

a review key in the JSON file, but the actual implementation was using

reviews. review is much more appropriate, so I've changed the

implementation to match the documentation.
This also adds issue_opened as a field for general comments in the

documentation. Because of how we create comments, any field that's valid

for the comment resource will work, but it was confusing to list

issue_opened under diff comments but not general comments.

Posted a review using rbt status-update set that included body top and

body bottom content, and saw that that content was properly reflected in

the rendered status update.