Find some how-to-github material for newcomers and link it in the readme

[yk]

There are people coming from e.g. GitLab who could use an introduction on GitHub forks & PRs.

[kiritowu]

Github's documentation on "Collaborating with pull requests" seems like a good introduction.

Some important ones are:

• About forks
• Fork a repo
• Syncing a Fork
• Creating a pull request from a fork

[yk]

thank you! could you make a PR and put that into the readme? I know, very meta ;)