update pre-release docs

[sssoleileraaa]

Status

Ready for review / Work in progress

Description of Changes

Fixes #.

Changes proposed in this pull request:

Testing

How should the reviewer test this PR?
Write out any special testing steps here.

Deployment

Any special considerations for deployment? Consider both:

1. Upgrading existing production instances.
2. New installs.

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

[lgtm-com]

This pull request introduces 1 alert when merging 82ce80a into 309f17e - view on LGTM.com

new alerts:

• 1 for Unreachable code

[lgtm-com]

This pull request introduces 1 alert when merging cb6e56f into 4c5f1d1 - view on LGTM.com

new alerts:

• 1 for Unreachable code