knowledge_pad: link to forum instead of inactive mailing list

bt5/erp5_knowledge_pad/SkinTemplateItem/portal_skins/erp5_gadget/ERP5Site_viewAnonymousDocumentationGadget.zpt

@@ -8,6 +8,7 @@
   <p>Are you using ERP5 in your business? 
      If so please let us know if you would be 
      interested to provide us with some information 
-     by sending an email to erp5-users@erp5.org</p>
+     by posting on <a href="https://www.erp5.com/forum/">ERP5 Forum</a></p>
+
 
 </div>