minimal set of files from govuk opsmanual
update references for rps alpha
update references to rps in conf.py
add helper in makefile to open on mac
tidy up readme, etc
superficial tweak to bgcolor
adding the github ext in case needed
Add 'manual/' from commit '2f020603d3ee48035b7aaf03db96e1d71db5bfdc'

git-subtree-dir: manual
git-subtree-mainline: 7b9fd5000bbec08c33ef2828e3a855d5562bcea4
git-subtree-split: 2f020603d3ee48035b7aaf03db96e1d71db5bfdc