FATES master branch renamed to main

[glemieux]

The FATES software team has finally renamed the official NGEET repo master branch to main. Github automatically handles the retargeting of pull requests so if you have a PR open to fates you do not need to worry about adjusting the PR. You will need to change your local repository master branch name, however, so that you can continue to pull in updates from main. I've written up instructions for doing so in the QnA section of the FATES Github repository. Please feel free to respond to that discussion thread with any clarifications or questions you may have.