Update release notes for 7.x-2.x

In #2342619: D8 Version and queue gardening it is mentioned that the minimum requirements for getting the SQL server driver working for Drupal are:

ODBC 11: https://www.microsoft.com/en-us/download/details.aspx?id=36434
Wincache >= 1.3.7.4 : http://www.iis.net/downloads/microsoft/wincache-extension
PDO >= 3.2.0.0 : https://msdn.microsoft.com/en-us/sqlserver/ff657782.aspx

I think that gives us reason enough to update the release notes for the dev and any stable release of the 2.x branch of this driver so that we are providing the proper guidance to developers that are intending to use MS SQL Sever for their backend of the drupal site. I recently lost a lot of time tracking this information down. I would like to save the next developer some time in providing these details to them.