Write an outcomes section into the wiki

- https://github.com/alphagov/smartdown/wiki/Outcomes
- There was no spec about outcomes in the main readme as far as I could tell, so the wiki example is my best first round shot at attempting to explain the concept. (Basically, end pages.)
Move the rest into a pseudoglossary

- There's loads of OTT technical info in here, let's move it to a holdall glossary
- Additional wiki sections can be broken out and created from what's in there, but this would be a lot of work within this particular story
Add stub sections on dependencies and running

- As per the styleguide for READMEs here: https://github.com/alphagov/styleguides/blob/master/use-of-READMEs.md
Strip the markup down to reduce horizontal scroll