Add privacy link to helpfulness prompt (#16496)

* Add link

* Tweak spacing

includes/helpfulness.html

@@ -4,9 +4,13 @@
     data-help-start
     data-help-yes
     data-help-no
+    class="mb-1"
   >
     {% data ui.helpfulness.able_to_find %}
   </h4>
+  <p class="f6">
+    <a href="/site-policy/github-privacy-statement">Privacy policy</a>
+  </p>
   <p
     class="radio-group"
     data-help-start