[ci-skip][docs] Fix rich_text_area to rich_textarea in getting_started.md

Author: hachi8833

guides/source/getting_started.md

@@ -1756,7 +1756,7 @@ description in `app/views/products/_form.html.erb` before the submit button.
 
   <div>
     <%= form.label :description, style: "display: block" %>
-    <%= form.rich_text_area :description %>
+    <%= form.rich_textarea :description %>
   </div>
 
   <div>