add watermark partial

Author: osfameron

src/partials/watermark.hbs

@@ -0,0 +1,12 @@
+{{#with page.attributes.watermark}}
+<div id="watermark">{{this}}</div>
+{{/with}}
+{{#if page.attributes.show-preview-banner}}
+<div class="article-banner">
+<i class="fas fa-cog"></i>
+<h2>{{#with page.attributes.watermark}}<tt>{{this}}</tt>
+{{else}}Preview{{/with}}</h2>
+<p>You are viewing a preview version of the documentation.</p>
+<p>Visit the <a href="{{ site.url }}/doctor/tree.html">preview landing page</a> for more details.</p>
+</div>
+{{/if}}