Add new canonical page describing GitHub teams and access policy

There was a lack of documentation regarding which teams are
available in GitHub and what they are intended for. There was also
duplication of instructions for how to request access, so I've
consolidated that here and will remove references from elsewhere
in subsequent commits.

source/manual/github-access.html.md

@@ -0,0 +1,44 @@
+---
+owner_slack: "#govuk-2ndline-tech"
+title: GitHub access
+parent: "/manual.html"
+layout: manual_layout
+section: Accounts
+---
+
+## Do you need GitHub access?
+
+Not everyone on GOV.UK requires GitHub access, as much of what we do is in the open. However, if your role requires it, you can be added to the alphagov org.
+
+If you're a content designer, your request should go through Zendesk (see [example ticket](https://govuk.zendesk.com/agent/tickets/5297731/events)).
+
+If you're an engineer or contractor, ask a developer on your team who has production access (such as your tech lead) to follow the steps below. If no developers on your team are available, ask in the [Technical 2nd Line Slack channel](https://gds.slack.com/archives/CADKZN519) for someone to add you.
+
+## Granting GitHub access
+
+These steps should only be completed by a developer with production access:
+
+1. Add the person to the relevant file in [govuk-user-reviewer](https://github.com/alphagov/govuk-user-reviewer).
+1. Email <govuk-github-owners@digital.cabinet-office.gov.uk>, asking for the person to be added to the org. You should include:
+  1. A link to the pull request created in the previous step.
+  1. The GitHub username to be added.
+  1. The name of the team they should be added to (see [Teams in alphagov](#teams-in-alphagov)). This is usually "GOV.UK" for engineers and contractors, and "GOV.UK Content Designers" for content designers.
+  1. An explanation of which team the person is working in, and in what role.
+1. An alphagov admin will process the request. The person will receive an invite from GitHub in their inbox, which they will have to accept.
+
+## Teams in alphagov
+
+There are several core 'teams' set up in GitHub, under the [alphagov org](https://github.com/orgs/alphagov).
+
+- [GOV.UK Content Designers](https://github.com/orgs/alphagov/teams/gov-uk-content-designers/members).
+  This team allows the user to create a branch in a GOV.UK repository and open a pull request, but only a developer can merge the request.
+  Only content designers should be added to this team.
+
+- [GOV.UK](https://github.com/orgs/alphagov/teams/gov-uk).
+  This team gives write access to private repos (see [Configure a GitHub repo](/manual/configure-github-repo.html)), as well as integration admin access to the CI environment.
+
+- [GOV.UK Production Deploy](https://github.com/orgs/alphagov/teams/gov-uk-production-deploy).
+  Grants [deploy access to staging and production](/manual/rules-for-getting-production-access.html#production-deploy-access).
+
+- [GOV.UK Production Admin](https://github.com/orgs/alphagov/teams/gov-uk-production-admin).
+  Grants [admin access to staging and production](/manual/rules-for-getting-production-access.html#production-admin-access).