Add link to footer containing link to page source

In order to make it easier for users to discover where to edit the
website, add a link in the page footer pointing to the current page in
GitLab.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>

config.toml

@@ -26,6 +26,7 @@ languageCode = "en-us"
   rss = true
   license = "Content is available under Creative Commons Attribution Share Alike unless otherwise noted."
   pager = false
+  sourceLink = "https://gitlab.apertis.org/docs/apertis-website/-/blob/master/content/"
 
 # Menu
 [menu]

themes/beautifulhugo/layouts/partials/footer.html

@@ -60,6 +60,9 @@
           {{ end }}
           </ul>
         </p>
+        <p class="credits text-center text-muted">
+            <a href="{{ $.Site.Params.sourceLink}}{{ $.File.Path }}">View page source</a>
+        </p>
 
         <!-- Please don't remove this, keep my open source work credited :) -->
         <p class="credits theme-by text-muted">