Make the instructions more welcoming for non-government

There are a number of influential and interested individuals who don't have government-issued email addresses e.g. retirees, collaborators in academia, concerned citizens.
Merge pull request #257 from github/relax-entry-criteria

Make the instructions more welcoming to those with non-government emails
A quick summary of GDS blog post about git/github

A summary of the blog post I wrote for the GDS technology blog on how we use git/github and a link out to it.
Update title for those who may not know about GDS

As per @benbalter's feedback
add image to uk post, bump date to today
forgot to remove renamed GDS post
Merge branch 'gh-pages' into accessibility