Set up build-system wiki contribution process

At this moment, anybody (with permissions) can edit the content of the [build-system wiki ](https://github.com/AlmaLinux/build-system/wiki), and until now, we've been using hackmd.io or other stuff for reviewing them. Ideally, anybody could create PRs against the wiki in the same way we create PRs for reviewing source code.

We can use this article as inspiration: https://nimblehq.co/blog/create-github-wiki-pull-request