Add self-link to each documentation topic.

Frustratingly is-small has no effect when inside a title/subtitle
element. I wanted to put it immediately after the title, but then it was
distractingly huge.

Author: jdblischak

layouts/docs/summary.html

@@ -1,5 +1,14 @@
 
-  <h2 class="title is-h2" id="{{ .Title | urlize }}">{{ .Title }}</h2>
+  <h2 class="title is-2" id="{{ .Title | urlize }}">
+    {{ .Title }}
+  </h2>
+  <p class="subtitle">
+    <a href="#{{ .Title | urlize }}">
+      <span class="icon is-small">
+        <i class="fas fa-link"></i>
+      </span>
+    </a>
+  </p>
   <div class="content">
     {{ .Content }}
   </div>