Release notes 12-9

@mhoeber @lamagnifica @catong Please review.

@clintonb Since you're release lord (should that be capitalized?) this week, you get a sneak peek at the release notes. You don't have to do a thorough review, but feel free to read through them and let me know if anything seems amiss.
separate confuses me each time I read this. Is it currently a single process? If so, maybe rephrase in the first sentence so that the structure doesn't emphasize two sequential steps. Or, maybe it was always two processes and now they can be completed independently of each other?