Adds “Edit on GitHub” link

[kennethormandy]

Hey! Awesome work on this site, it looks great. This pull request adds a little snippet we use on the Harp docs to let people know they contribute.

The link will fork the project for them and open up the editing view on GitHub. Feel free to use as much or as little of this as you’d like :)

[alexwolfe]

@kennethormandy this is a cool idea and thanks so much for the contribution. However, I don't want folks to exit the flow on this page to github. The the next CTA will be geared toward viewing the guide in order to continue the learning process.

We have already given top billing to "Contribute" in the main navigation. It's now one of only 4 links in the navigation (25%) which I think it exceptionally high priority given the real estate.

That said, perhaps there is a more subtle way to include something like this. I'm going to close this pull for now but play around with designs ideas that could work for incorporating something like this. Again, great idea, l'll def play around with this.

[kennethormandy]

Cool! That totally makes sense. I mostly just wanted to share the snippet, if it comes in handy later on that’s great too.

[alexwolfe]

Thanks @kennethormandy I'm sure it will. Appreciate you sharing this 👍