Improve help message

core/src/main/resources/hudson/tasks/Mailer/help-url.html

 <div>
   Optionally specify the HTTP address of the Jenkins installation, such
   as <tt>http://yourhost.yourdomain/jenkins/</tt>. This value is used to
-  let Jenkins know how to refer to itself, ie. for links to images and
-  links in emails.
+  let Jenkins know how to refer to itself, ie. to display images or to
+  create links in emails.
 
   <p>
   This is necessary because Jenkins cannot reliably detect such a URL