Merge Prep: Update README & add merge guidance comment to src.pro

As the changes to the project file won't auto-merge I have tested
what needs to be done with meld or kdiff3 to combine the two specified
branches in the proposed order and provided guidance as a (deleted after
performing) comment at the top of the file.

(A previous attempt to do ended up with the comment in the wrong branch's
copy of the file...!)

Signed-off-by: Stephen Lyons <slysven@virginmedia.com>