ISSUE(number) should append, not replace, the description

[fantasai]

I noticed that with

ISSUE(number): something something

any commentary in the spec gets dropped and replaced by a dynamically-generated issue title. I think it would be better if this syntax did not delete any in-spec commentary, but just appended the link to the issue.

[svgeesus]

Particularly with issues that started off inline and then got migrated out to GH, I notice that something something either ends up being the issue title, or the body of the first comment.

In the former case, replacing something something with the actual title (which may change over time) is helpful. In the latter case, dropping something something means you actually have to follow the link to GH to find what it is about. So I agree that appending would allow a well-crafted, short summary to be retained.

[fantasai]

@svgeesus Fwiw, I fixed up the handling of github issues when "Inline Github Issues" is false so it looks nicer in https://github.com/tabatkins/bikeshed/pull/2143 (see example) so I've switched css-values-4 to using that.