replaced link to imsc REC, not for release but for future use

[himorin]

This PR is not for immediate release, but to be used on future release by edited or amended recommendation (not in-place edits).

---

Preview | Diff

[nigelmegitt]

@palemieux interesting point. I don't know the answer, but I agree it would be good to have the GitHub match the published Rec.

[nigelmegitt]

I'm certainly happy to have this match modulo the boilerplate, noting also that the publication date is also wrong - on the /TR version it is 08 November 2018, but on the preview here it shows up as 01 June 2020, when I look at it now, despite having the correct publishDate.

Respec issues we could consider opening (and I checked are not currently open):

• allow a historical publish date,
• allow <aside>s with a specified class to be inserted before auto-generated text such as for <section id="sotd">