Only show title in col 1 until both docs selected.

sourcing/templates/build_links.html

@@ -57,8 +57,11 @@ body, html {
 <div>
 <div class="col col1">
   <h3>Link builder</h3>
-  <p>Select something in the first document.</p>
-  <button class="btn btn-primary" id="new-link">confirm selection</button>
+
+  {% if doc1 and doc2 %}
+    <p>Select something in the first document.</p>
+    <button class="btn btn-primary" id="new-link">confirm selection</button>
+  {% endif %}
 
 </div>
 <div class="col col2">