Ahodges/doc/relnotes20141021

@mhoeber , @catong , @srpearce please take a look -- anything else to add? 
@explorerleslie , @shnayder ?
Oh, that's very helpful - thanks!

From the original text, I thought a message box would appear. Since it's just text in the UI, maybe something like this:

When you mark a response to a question post as a correct answer, the following text appears above the text of the correct answer:

`marked as answer less than a minute ago by <username>`

You can click the username in the message to open a new page that lists all the contributions that user has made to the course discussions.

(maybe an image here?)