update pre-release docs - part 3

[sssoleileraaa]

Status

Ready for review

Description of Changes

Update RM docs to include details around the beginning steps of the pre-release process.

Testing

Someone who's familiar with release management should make sure the changes are accurate and helpful.

Checklist

If you made changes to the server application code:

• Linting (make lint) and tests (make test) pass in the development container

If you made changes to securedrop-admin:

• Linting and tests (make -C admin test) pass in the admin development container

If you made changes to the system configuration:

• Configuration tests pass

If you made non-trivial code changes:

• I have written a test plan and validated it for this PR

If you made changes to documentation:

• Doc linting (make docs-lint) passed locally

If you added or updated a code dependency:

Choose one of the following:

• I have performed a diff review and pasted the contents to the packaging wiki
• I would like someone else to do the diff review

[conorsch]

Wonderful, very clear. Thank you for taking the time, @creviera !