As you can see on the top of this page, you can add "Edit on Github" links to your pages, this feature can be enabled with a single parameter.

The value has to be the path to the root of your documentation folder in your repository.

In the value you see below, Daux's documentation is in the docs folder in the master branch.

Daux.io will handle the rest

{
    "html": {
        "edit_on_github": "justinwalsh/daux.io/blob/master/docs"
    }
}