Added a branch project rule to the pre-commit so that it complains if you try to commit directly to main. I figure folks who really need to push to main also know how to work around it. based on convo in call w/ @greglucas

Not quite sure this is the best way to handle the error message but figure we need to give folks a fix.
Um sorry, did not mean to open this branch on the mpl repo. (Also don't know how I did that since I branched from my local fork 😦)