ZA: Document update_za_hansard.bash and friends

Documents the scripts run by update_za_hansard.bash, which are
supplied by the za-hansard project
Merge branch 'issues/1228-document-hansard' of ssh://git.mysociety.org/data/git/public/pombola
Add links to social icons in ZA footer
Merge branch 'issues/1167-footer-social-links' of ssh://git.mysociety.org/data/git/public/pombola
Merge branch 'master' into staging-auto-deployed