[ttml2] Add summary of changes wrt TTML1

nigelmegitt has just created a new issue for 
https://github.com/w3c/ttml2:

== Add summary of changes wrt TTML1 ==
Was 
[Action-364](https://www.w3.org/AudioVideo/TT/tracker/actions/364):

* to add an editorial note to the introduction describing the 
differences relative to TTML1.

Please view or discuss this issue at 
https://github.com/w3c/ttml2/issues/154 using your GitHub account

Received on Tuesday, 15 March 2016 17:07:38 UTC