Chore/update readme and hardening manifest

What is your Merge about?

If this is your first merge, please use the Initialization Template.

This is updating the README and hardening manifest with new maintainers.

For more information please visit Iron Bank Documentation

Note: Please be sure you create an issue related to this merge request and the issue is labeled ~"Hardening::Review", this will initiate a CHT member review of your merge request.