[#36] Add help text for the Newsletter Double-Opt-In setting

templates/CRM/Twingle/Form/Profile.hlp

@@ -38,6 +38,10 @@
     {ts domain="de.systopia.twingle"}Select which financial type to use for recurring contributions.{/ts}
 {/htxt}
 
+{htxt id='id-newsletter-double-opt-in'}
+    {ts domain="de.systopia.twingle"}Select whether to use CiviCRM's Double-Opt-In feature for subscribing to mailing lists. Note that this only works for public mailing lists. Any non-public mailing list selected above will be ignored when this setting is enabled.{/ts}
+{/htxt}
+
 {htxt id='id-membership-postprocessing-call'}
     {ts domain="de.systopia.twingle"}Some organisations have specific conventions on how a membership should be created. Since the Twingle-API can only create a "bare bone" membership object, you can enter a API Call (as 'Entity.Action') to adjust any newly created membership to your organisation's needs.{/ts}
     {ts domain="de.systopia.twingle"}The API call would receive the following parameters:<ul>

templates/CRM/Twingle/Form/Profile.tpl

@@ -214,7 +214,24 @@
         </tr>
 
         <tr class="crm-section">
-          <td class="label">{$form.newsletter_double_opt_in.label}</td>
+          <td class="label">
+            {$form.newsletter_double_opt_in.label}
+            <a
+                    onclick='
+                            CRM.help(
+                            "{ts domain="de.systopia.twingle"}Newsletter Double Opt-In{/ts}",
+                    {literal}{
+                      "id": "id-newsletter-double-opt-in",
+                      "file": "CRM\/Twingle\/Form\/Profile"
+                    }{/literal}
+                            );
+                            return false;
+                            '
+                    href="#"
+                    title="{ts domain="de.systopia.twingle"}Help{/ts}"
+                    class="helpicon"
+            ></a>
+          </td>
           <td class="content">{$form.newsletter_double_opt_in.html}</td>
         </tr>