Rewrite of Devops

Updated for style - removing banned words, inserting bullet lists etc.
Helpdesk rewrite for style

Update/rewrite for style: bullets, caps, banned words, tone of voice etc.
Rewrite of guidance for style

removed banned words, changed layout (inserting bullet lists), active tone etc.
minor style change
Rewrite of content for style

removing banned words, using bullet lists, being more direct with tone etc.
Rewrite of guidance for style

Removing banned words, using bullet points, active voice etc.
Rewrite of guidance for style

removing banned words, using bullet lists, other style points
Rewrite of guidance for style
hyphen for error-prone
em dash
Capitalise Devops

That's how Patrick defined it.
Improve CESG links

- Fix broken links :(
- Remove expanded version of CESG
- Prefer HTTPS
Tweak text

Remove reference to silos, which are mentioned in the previous
paragraph.
Prefer '--' to '–'
Merge pull request #336 from alphagov/ops-revision-updated

Ops revision (updated)