Start using branch 'master' instead of 'gh-pages' and deploy using GitHub Actions

[ottok]

Due to historical reasons GitHub pages required that the contents was on a branch named gh-pages. I suspect this is not required anymore, not at least if GitHub pages deployment is done using GitHub Actions.

TODO:

• [ ] Rename branch gh-pages to master to follow the convention of regular git repos
• [ ] Activate GitHub Actions to deploy from master to seravo.com/docs: https://github.com/Seravo/docs/actions/new

[ypcs]

No need to use actions, branch is nowadays selectable directly from repo settings: https://github.com/Seravo/docs/settings

[ottok]

Thanks for noticing. GitHub Pages branch changed and repo default branch renamed from gh-pages to master in repo settings.