Grammar fix

The sentence sounded odd.

htroot/ConfigRobotsTxt_p.html

@@ -10,7 +10,7 @@
     <h2>Exclude Web-Spiders</h2>
     <p>
       Here you can set up a robots.txt for all webcrawlers that try to access the webinterface of your peer.
-      <span class="tt">robots.txt</span> is a volunteer agreement most search-engines (including YaCy) follow.
+      <span class="tt">robots.txt</span> is a voluntary agreement most search-engines (including YaCy) follow.
       It disallows crawlers to access webpages or even entire domains.
     </p>
     #(error)#