Website branch renaming

[Guillaume Smet]

Hi,

We renamed the branches of the website repository: https://github.com/quarkusio/quarkusio.github.io .

`develop` -> `main`

`master` -> `gh-pages`

The main change for you is that you now need to pull from `main` instead of `develop` from now on.

I had very specific instructions from Holly to say that if all went well it was thanks to her and if things went bad, it was all my fault.

Given it apparently is going well, you can thank Holly for the change, especially since she did most of the work :).

We will very soon push additional pull requests in the workflows that are consuming the website outside of this repo.

Thanks!

--

Guillaume