Add feedback link to the default layout (#499)

* troubleshooting API

* Revert to gerund

Though the style guide says to just use imperatives, "get started" just sounds weird. Also this is more consistent with "troubleshooting"

* fixed egregiously out-of-date info and added mention of Sheets to the concepts doc

* overhaul Sheets index page

* fix few mis-wordings

* restore mention of Workspace Marketplace

* tweak procedure

* Revert "tweak procedure"

This reverts commit d35bc34.

* tweak procedure again

* rewording suggested by Julia

* removed reference to video which I removed, and correct column number

* rewrote sort step of sleep tutorial

* updated data to 2020

* tweak images

* small tweaks

* redoing Covid tutorial

* more corrections to tutorials

* more tweaks

* Added feedback link to default layout

* changed wording

* fix tagging

_layouts/default.html

@@ -151,7 +151,13 @@
             {% endunless %}
             {{ content }}
           </div>
-        </div>
+          <div style="text-align:center" id="feedback-form">
+             <p>
+              <a target="_blank" href="https://docs.google.com/forms/d/e/1FAIpQLSf23mC17idzIpzg6v4frCh8iWTl9dxeb4iSTVgo0WiBvnv5ZA/viewform?usp=pp_url&entry.871991796={{ page.url }}">
+              Send feedback about this page
+              </a>
+            </p>
+          </div>
       </div>
     </main>