Add a feedback mechanism to the Docs pages

[thisisjofrank]

Users should be able to feedback on whether the page was valuable, and should be able to easily make PRs on particular pages with a 'edit this on github' type link, which goes straight to the particular page.

Much like what Github have on their documentation

[thisisjofrank]

Feedback is now live on the site

[dandv]

should be able to easily make PRs on particular pages with a 'edit this on github' type link

Was this implemented by #342, or a different implementation? Asking because I'm running into links that point to the wrong files.