"Edit on GitHub" button should link to the specific markdown file for that page

**Current behavior**

The docs.px.dev site contains an "Edit on GitHub" button in the bottom-right hand side of the footer. Clicking this button will take you to the top-level folder in this repo, no matter what page you are on in the docs site.  

**Desired solution**

Ideally, the "Edit on GitHub" button would link to the markdown file for the specific content page that is open.  