"getting-started.md" is incomplete

[BigMood42069]

The "getting-started.md" readme is missing it's 3rd section, "connecting-to-an-existing-repository-that-already-has-the-github-for-unity-package"

Is it in another .md file or have I missed something that already tells me this info? Either way, I would like to have either the section added in or a link to another .md file that has that information.