Support GitHub linking

I feel like it's common for the widgets developed within a Parade-like environment to also live within GitHub for most consumers. It would be nice to support linking between a GitHub repository and a given Parade instance. This would allow users to click "edit" buttons on examples, for instance, which would take the user to GitHub to fork the repository, etc. This could most likely be driven through configuration.

Start by locating the widget examples' "edit" controls and the configuration entry points that could hold a GitHub repository link. Trace how an edit action is rendered and define done as configuring a repository link that takes users to GitHub to fork or edit the relevant example.

Written by the indexing model from the issue text.