cgroups.html.in: Kill useless spaces in <pre/>

The <pre/> section is rendered as-is on the page. That is, if all
the lines are prefixed with 4 spaces the rendered page will also
have them. Problem is if we put a box around such <pre/> because
the content might not fix into it.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

docs/cgroups.html.in

@@ -221,11 +221,11 @@ $ROOT
     </p>
 
     <pre>
-  ...
-  &lt;resource&gt;
-    &lt;partition&gt;/machine/production&lt;/partition&gt;
-  &lt;/resource&gt;
-  ...
+...
+&lt;resource&gt;
+  &lt;partition&gt;/machine/production&lt;/partition&gt;
+&lt;/resource&gt;
+...
     </pre>
 
     <p>