Rename master branch to main

[ncoghlan]

Pull request queue is clear, so taking the opportunity to rename the master branch to main.

[ncoghlan]

@hugovk Actually, it looks like I don't have enough rights on the repo to do that (presumably related to the long ago migration from my personal account to the Jazzband umbrella org). No Settings tab, and attempting to change the branch name just tells me I don't have the required permissions.

[hugovk]

Yeah, it needs an admin, see https://github.com/jazzband/help/issues/196.

[ulgens]

@ncoghlan Sorry for the edit on your comment. I saw the "add tasklist" button and I thought it's going to create something new, but instead it edited your content. I have no idea how and why I've this permission.