Icinga howto version update

Doc/Sdi/Icinga/icinga.xml

@@ -11,15 +11,15 @@
          xmlns:db="http://docbook.org/ns/docbook">
   <title>Icinga</title>
 
-  <para>With respect to more current modules we start from the more recent
-  <link xlink:href="https://packages.icinga.com/debian/#indexlist">icinga2
-  packages</link>.</para>
+  <para>We start from <link
+  xlink:href="https://packages.icinga.com/debian/#indexlist">icinga2
+  packages</link>:</para>
 
   <itemizedlist>
     <listitem>
       <para><link
-      xlink:href="https://www.howtoforge.com/tutorial/how-to-install-icinga2-on-debian-9">How
-      to Install Icinga 2 Monitoring Tool on Debian 9.2</link></para>
+      xlink:href="https://www.howtoforge.com/how-to-install-icinga-2-monitoring-software-on-debian-11">How
+      to Install Icinga 2 Monitoring Software on Debian 11</link></para>
 
       <caution>
         <para>Fix <code>admin</code> email in