Should be easier to edit the doc

[ptbrowne]

To have the most up-to-date doc, we should make it easier to edit the doc, for now it is a bit cumbersome since we need to find the markdown to edit etc..

Mkdocs has an { edit_uri } variable that is used to do that. It could be used to add a link under the menu.

The only problem would be for the external docs since the markdowns are not in the cozy-docs-v3 repository. A bit of JS executed at page load could check if it is an external repository and update the href of the link.

[clochix]

I thought we used edit_uri to provide a direct link to edit every page, but it looks like the link has been removed from the template ☹