More specific docs link

No issue

Nothing wrong with the docs link but in this context makes more sense to deep link to the info specifically about Ghost Handlebars themes

app/templates/settings/design.hbs

@@ -95,7 +95,7 @@
                         </div>
                     </div>
                 </a>
-                <a class="td-cta-box td-cta-docs" href="https://docs.ghost.org" target="_blank" rel="noopener">
+                <a class="td-cta-box td-cta-docs" href="https://docs.ghost.org/api/handlebars-themes/" target="_blank" rel="noopener">
                     <div class="td-cta-icon">{{svg-jar "book-open"}}</div>
                     <div class="td-cta-content-wrapper">
                         <div class="td-cta-content">