Add support for new contributor frontmatter object

includes/article.html

@@ -20,6 +20,12 @@ <h1 class="border-bottom-0">{{ page.title }}</h1>
         </div>
       </div>
 
+      {% if page.contributor %}
+        <div class="partner-callout border rounded-1 mb-4 p-3 border-blue bg-blue-light f5">
+          <p>This page is kindly contributed and maintained by <a href="{{ page.contributor.URL }}" rel="nofollow">{{ page.contributor.name }}</a>.</p>
+        </div>
+      {% endif %}
+
       {% if page.intro %}
         <div class="lead-mktg">{{ page.intro }}</div>
       {% endif %}

lib/frontmatter.js

@@ -119,6 +119,14 @@ const schema = {
     defaultPlatform: {
       type: 'string',
       enum: ['mac', 'windows', 'linux']
+    },
+    // Documentation contributed by a third party, such as a GitHub Partner
+    contributor: {
+      type: 'object',
+      properties: {
+        name: { type: 'string' },
+        URL: { type: 'string' }
+      }
     }
   }
 }