Review and update documentation

[eouthwaite]

This is something of a catch-all to replace #83 as we are not following the original sprints

Would we be better off moving the documentation out of the code and into the Wiki tab?

[eouthwaite]

From #82 :
Ensure all 'how it works' documentation reflects how it has ended up working.
Ensure all steps are covered in STEPS.md
Ensure complex tasks are documented in documentation/features with their own documentation
Update install guide for changes (especially security)

[eouthwaite]

also relates to #141

[eouthwaite]

RESTAPI.md would be better if more like swagger documentation with example payloads and results