Encourage writers to open the linter when editing MDN

[a2sheppy]

Could the add-on be enhanced so that when the user is in MDN's editor, it adds a little blurb or box or something somewhere to remind the user to open the sidebar and run the linter? Perhaps add an "open linter sidebar" button next to the Save buttons on the page (and ideally to the CKEditor toolbar, if that's possible without a CKEditor plugin -- if one is required I might be able to help with that).

If an "open linter" button can't be done, at least a text reminder to use the linter would be helpful -- I keep forgetting to do it! :)

[MatonAnthony]

This one should be possible once https://bugzilla.mozilla.org/show_bug.cgi?id=1341126 land on Nightly.