docs: old version release instructions

[MikeMcC399]

Situation

CONTRIBUTING > Publishing images contains a brief paragraph concerning releasing old versions:

In general, factory/.env master should contain the latest versions we officially support. If you need to release an older version please modify circle.yml to push releases from a feature branch instead of setting the version in master to older versions.

factory/.env contains more detailed comments.

Following these instructions would move latest tags to older versions and could also move a cypress/included<short tag> to an older version.

Changes

• Instructions to suppress creating latest and cypress/included<short tag> tags for the release of older versions are added.
• Typos and other inaccuracies are tidied up.
• Advice for the naming of a feature branch is given.

[cypress-app-bot]

• Create a Draft Pull Request if your PR is not ready for review. Mark the PR as Ready for Review when you're ready for a Cypress team member to review the PR.

[MikeMcC399]

Preview

• https://github.com/MikeMcC399/cypress-docker-images/blob/old-version-release/CONTRIBUTING.md#publishing-images
• https://github.com/MikeMcC399/cypress-docker-images/blob/old-version-release/factory/.env
• https://github.com/MikeMcC399/cypress-docker-images/blob/old-version-release/factory/docker-compose.yml
• https://github.com/MikeMcC399/cypress-docker-images/blob/old-version-release/circle.yml