chore: Add warning that not all field types are supported

Author: smessie

app/templates/index.hbs

@@ -24,6 +24,7 @@
     </div>
     <small id="load" class="form-text text-muted">When loading a form resource, any changes will be discarded and the
       given URI will be loaded.</small>
+    <p class="text-warning"><strong>Beware!</strong> This is only a proof of concepts, not all field types by the vocabularies are supported.</p>
   </form>
 
   {{#if this.success}}