Rename master to main?

[bjlittle]

Given the migration of the community and git tooling away from master to main, are there any opinions on whether nc-time-axis should adopt this rebrand?

See here for further details.

Now, if any, seems like a very apt time to decide on this.

What do you think @SciTools/nc-time-axis-devs ? 🤔

[trexfeathers]

Needs to happen