Add FutureLearn to work snip

This will appear at the top of our list of recent work on the homepage
and at /work.
Update the wording of the futurelearn snip

Based on feedback from @floehopper in pull request 24[1].

[1] https://github.com/freerange/site/pull/24
Merge branch 'add-futurelearn-to-work-snip'

This adds a couple of paragraphs about the work we did with FutureLearn.