Rename master branch to main

[graeme-a-stewart]

As there's been a lot of discussion in many communities about the conotations of git's default master branch (which I don't want to repeat here), but I'd like to propose that we rename the development branch of hsf.github.io to main which is a very acceptable alternative.

It's rather easy to do, following instructions like this: https://github.com/github/renaming.

[klieret]

Any update @graeme-a-stewart ?

[klieret]

Pushing for a this, just because all of my muscle-memory meanwhile does checkout main ;)

[hegner]

@graeme-a-stewart - will bring that up in the next coordination meeting, And then just execute...

[adi-develops]

Hi! Please assign this issue to me. I can rename the master branch to main. I also think it would be more convenient.