captive portal, enforce local group, add note, closes https://github.com/opnsense/core/issues/1503

src/opnsense/mvc/app/controllers/OPNsense/CaptivePortal/forms/dialogZone.xml

@@ -30,7 +30,8 @@
         <id>zone.authEnforceGroup</id>
         <label>Enforce local group</label>
         <type>dropdown</type>
-        <help><![CDATA[Restrict access to users in the selected (local)group.]]></help>
+        <help><![CDATA[Restrict access to users in the selected (local)group. <br/>
+        <b>NOTE:</b> please be aware that users (or vouchers) which aren't administered locally will be denied when using this option.]]></help>
     </field>
     <field>
         <id>zone.idletimeout</id>