Add Freebies on-boarding email text

- ref: https://github.com/GigaOM/legacy-pro/issues/4368
instead of assigning a value into `$expire` here and then assign 'END_DATE' key to `$expire`, why not just assign `END_DATE` to `$exp->format( 'm-d-Y' )` below directly?

Also what about a more human-readable format, like 'F dS, Y' (would output something like 'October 16th, 2014')?