Use bootstrap warning for disclaimer

Author: Mark Robinson

src/main/resources/templates/index.html

@@ -38,7 +38,9 @@ <h1>Common Workflow Language Viewer</h1>
                         <a href="https://researchobject.github.io/specifications/bundle/" rel="noopener" target="_blank">
                             Research Object Bundle</a>
                         (zip file with metadata in a manifest), allowing it to be easily viewed and shared.</p>
-                    <p>This tool is currently experimental and may not work for all valid workflows.</p>
+                    <div class="alert alert-warning">
+                        <p><strong>Caution:</strong> This viewer is currently experimental and may not work for all valid workflows</p>
+                    </div>
 
                     <h2>Workflow from Github URL</h2>
                     <p>Provide a link to the directory of files making up your workflow here</p>