Add missing username tags.

svn path=/head/; revision=17199

en_US.ISO8859-1/books/handbook/disks/chapter.sgml

@@ -3115,7 +3115,7 @@ Filesystem        Size   Used  Avail Capacity  Mounted on
       <para>After each boot, any encrypted file systems must be
 	re-attached to the kernel, checked for errors, and mounted, before
 	the file systems can be used. The required commands must be
-	executed as user root.</para>
+	executed as user <username>root</username>.</para>
 
       <procedure>
 	<step>