Adding Support Policy + Doc Updates

[ericspod]

Addresses #8303.

Description

This adds language in the README.md file stating the support policy. There's a few things needing updating in documents that I've added as well. I've explicitly not mentioned versions of libraries in the README.md so that this doesn't go out of date, and just stated the update policy time window of support.

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.

[KumoLiu]

LGTM, thanks for the pr.

[KumoLiu]

/build

[KumoLiu]

/build

[ericspod]

Hi @jamesobutler I have added a notice about version support policy to the readme file here. This can be amended if there's anything you feel we should add or change.