Add rel=edit attribute to "Suggest an edit" link

[capjamesg]

This PR adds the rel="edit" attribute to the "Suggest an edit" edit link.

rel=edit lets a page indicate that the linked resource can be used to edit the page. It is defined at https://microformats.org/wiki/rel-edit. This can then be parsed by tools like the Universal Edit Button and custom bookmarklets to open the edit page corresponding with a website.

[ehuss]

Thanks, looks like the tests are failing, though.

@notriddle or @GuillaumeGomez are you familiar with rel="edit"? Does this seem like something worth adding?

[GuillaumeGomez]

Hum, not 100% sure it's ok (although I think it's fine). This button is to suggest an edit whereas the rel=edit docs say:

Tells the browser the URL for editing the current page

So not exactly the same but it's nitpicking here. Let's see if @notriddle has another opinion but I think it's ok.

[notriddle]

So not exactly the same but it's nitpicking here.

The Microformats wiki page links to the Suprabase Docs as a positive example, and they're using rel=edit to link to a GitHub editor page just like this PR proposes.

That seems like a positive endorsement of the practice. I'm fine with this change.