Simplify intro text and provide a very simple example

- Thought it would be good to show any new users what the outcome of using the DSL would be
- Shows an image of the final outcome within a GOV.UK sample page
- Will break into more complex concepts around logic as we go.
*NB:* My intention is to move the majority of the 'node' logic examples to the [wiki](https://github.com/alphagov/smartdown/wiki) so this readme just provides an intro, installation, test and running guides. All further info around specific tasks can sit in the wiki.
Add link to the wiki

- Adding this quite high up as readers may just wish to get to the implementation details immediately, having seen the intro speil before.
Quick reweite of the language para

- very minor clarification of language, probably just subjective here!
Change the language from 'cover sheet' to 'start page'

- We have Start Pages on GOV.UK and I think everyone is familiar with this terminology
- Not sure if there's a separate language within content teams wherein 'Start Page' gets translated into 'Cover Sheet', but I think 'Start Page' works for a broader range of people within a team.
- Adds liknks to wiki entries for start pages and questions. Placeholders for the other types
Move 'cover sheet', 'question' and 'choice' to the wiki

- They're at https://github.com/alphagov/smartdown/wiki/Start-Pages, https://github.com/alphagov/smartdown/wiki/Questions and https://github.com/alphagov/smartdown/wiki/Choices now
- Have also been rewritten to include examples of smartdown, html and rendered content
Move scenarios to the wiki

- https://github.com/alphagov/smartdown/wiki/Scenarios
- Just a quick shift over to the wiki, more work can be done on the page there.
Move country question to it's own wiki page

- https://github.com/alphagov/smartdown/wiki/Country-Questions
- Should have an example and a rendered outcome
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
fix question typo
Merge pull request #117 from alphagov/refactor/styleguide-led-readme

Change README to use alphagov readme styleguide