Restructure deployment doc to account for CD
Restructure deployment doc to account for CD

The previous structure was tied to our manual deployment
process. I've now created a 'Deployment' heading, with
'Continuous Deployment' and 'Manual Deployment' subheadings
beneath that.

I've removed some of the unnecessary callouts (>), as
overuse lessens their impact. I've also removed links
to specific automated checks such as linting, as this
isn't necessarily consistent across apps and can be easily
derived from looking at the application you're deploying.

alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs