Docs: Imply that the branch name is not optional
Docs: Imply that the branch name is not optional

The update checker will look for a `master` branch by default, but new repositories use the name `main` instead, and it is technically possible to use any branch as the default branch. So while you don't *have to* set the branch name, it's probably a good idea to always do that.
YahnisElsts/plugin-update-checker,YahnisElsts/plugin-update-checker