Comment on an issue, or comment in reply to an earlier comment on the issue.

Every issue can be viewed as a tree of comments, with the initial issue description at the root.

Discussions about the issue can be organized in sub-trees, by using `--reply-to`.

As a fallback, when `--reply-to` is not used, the comment will be in response to the issue description itself.

Using `--edit` preserves this structure of replies.