Master to Main README Update

[mcleo-d]

Description

This PR updates the CSC README.md to update repo visitors of the recent branch change from master to main.

README Addition

Important Notice

The CSC default branch has been renamed.

master is now named main

If you have a local clone, you can update it by running:

git branch -m master main
git fetch origin
git branch -u origin/main main
git remote set-head origin -a

Closes #119

[TLATER]

LGTM! People with more intricate local branches may want to use the script here: #119 (comment)

But I'll grant that that's too complex for a little readme entry :)

[TLATER]

As a minor nit, if you update the commit message to include Closes #119 in the body, it would automatically close that issue once it lands (which I think we want), and help with context for anyone diving into the history in the future.

[mcleo-d]

As a minor nit, if you update the commit message to include Closes #119 in the body, it would automatically close that issue once it lands (which I think we want), and help with context for anyone diving into the history in the future.

Thanks for clarifying the closes @TLATER. I wasn't sure if there were more tasks to complete on that issue first, but now I know we're good! 👍🏻

[mcleo-d]

LGTM! People with more intricate local branches may want to use the script here: #119 (comment)

But I'll grant that that's too complex for a little readme entry :)

@TLATER - I have added a link to your comment on commit 8d0ac2d