Document usage of the workflows in your own project

[NiklasEi]

Since this is the official example to point users to asking "how to add CI to my project", we should make it clear what might need to be changed in order to use the workflows in an already existing project.

[Polostor]

Nice work! IMHO it could be handy to give the notice that the GITHUB_TOKEN is created automatically with link to the Automatic Token Authentication as well though.. 🤔😉