What version are you running?
3.0.5
What's the URL of the page this enhancement relates to, if any?

Describe the enhancement and the motivation for it.
I would like to be able to add or modify a change-description after the fact (e.g. if I forget to write one before publishing the change).
By change I mean an review-request revision not the review-request itself (whose description can already be edited). I.e. the "text" field of a change entity as in https://www.reviewboard.org/docs/manual/2.5/webapi/2.0/resources/change-list/#webapi2.0-change-list-resource
What operating system are you using? What browser?
RHEL7/OSX

Chrome
Please provide any additional information below.
This would be zhweeeet :D