Making clear how to configure with debug messages.

refs #1877

doc/installation.texi

@@ -105,13 +105,18 @@ support, you can disable that by @command{./configure --enable-lto=no}.
 
 If you want to add debug messages, there are two steps to do that.
 First you have to enable modules, that you are interested in.
-Available are: server, zones, xfr, packet, dname, rr, ns, hash, compiler.
+Available are: @code{server, zones, xfr, packet, dname, rr, ns, hash, compiler}.
 You can combine multiple modules as a comma-separated list.
-For example: @command{./configure --enable-debug=server,packet}
-
 Then you can narrow the verbosity of the debugging message by specifying the
-verbosity as brief, verbose or details.
-For example:  @command{./configure --enable-debuglevel=verbose}.
+verbosity as @code{brief, verbose, details}.
+For example:
+@example
+$ ./configure --enable-debug=server,packet --enable-debuglevel=brief
+$ ./configure --enable-debug=server,packet --enable-debuglevel=verbose
+@end example
+
+
+For example:  @command{}.
 
 In most simple case you can just run configure without any options.