Fix broken link on Readme.md

Changed contribution guide to point to the file that is now in the main directory rather than the docs folder.
Merge pull request #1593 from kyconny/patch-1

Fix broken link on Readme.md
Slug change for UKTI Belgium.
Merge pull request #1594 from alphagov/ukti-belgium

Slug change for UKTI Belgium.
Change slug for charity commission.

Data migration to update the organisation slug, and associated data,
create a redirect and reindex documents in search.

This also renames the org screenshot file so that it can continue to be
found.
Merge pull request #1596 from alphagov/charity_commission_slug_change

Change slug for charity commission.
Merge pull request #1595 from alphagov/scheduled-publishing

Extract edition scheduled/unschedule service objects