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.
no. The affected courses were created on any date prior to December 4. The data for those courses is now available. The data that is available, regardless of when the course was created if before Dec 4th, begins on November 11.
better: 1st and last sentences, cut out the middle:
The enrollment activity chart, metrics, and report are now available
for courses created in Studio before December 4, 2013. EdX Insights 
now reports enrollment data for the affected courses beginning with 
November 11, 2013.