New guides for PRs and documentation

[theperu]

I improved the setup guide (going forward we might want to create specific guides for each OS but for now I kept it pretty minimal) and added the GitHub for beginners doc that we had on the Drive. I also created another page explaining how to contribute to the documentation. You can check how the pages will look like at:

• https://theperu.github.io/sossoldi/doc-guide.html
• https://theperu.github.io/sossoldi/PR-guide.html
• https://theperu.github.io/sossoldi/setup.html

[theperu]

As decided on Discord the PRs that are related to the documentation won't follow the standard review process at least for now so that we can update them faster. I'll merge this one for this reason