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": "dauxio/daux.io/blob/master/docs"
  }
}

Edit on other VCS

While GitHub is the most popular, it isn't the only, collaborative VCS out there.

As long as you can refer your files by a URL, you can create an edit link for your VCS with the following configuration:

{
  "html": {
    "edit_on": {
      "name": "Bitbucket",
      "basepath": "https://bitbucket.org/dauxio/daux.io/src/master/docs"
    }
  }
}