man: fix example formatting in systemd.preset

Repeating "example" everywhere was not useful, so remove
that and improve the formatting a bit.

man/systemd.preset.xml

@@ -136,23 +136,26 @@
   </refsect1>
 
   <refsect1>
-    <title>Example</title>
+    <title>Examples</title>
 
     <example>
-      <title>Default off example <filename>/usr/lib/systemd/system-preset/99-default.preset</filename>:</title>
+      <title>Default to off</title>
 
-      <programlisting>disable *</programlisting>
+      <programlisting># /usr/lib/systemd/system-preset/99-default.preset
+
+disable *</programlisting>
     </example>
 
     <para>This disables all units. Due to the filename prefix
     <literal>99-</literal>, it will be read last and hence can easily
-    be overridden by spin or administrator preset policy or
-    suchlike.</para>
+    be overridden by spin or administrator preset policy.</para>
 
     <example>
-      <title>A GNOME spin example <filename>/usr/lib/systemd/system-preset/50-gnome.preset</filename>:</title>
+      <title>A GNOME spin</title>
 
-      <programlisting>enable gdm.service
+      <programlisting># /usr/lib/systemd/system-preset/50-gnome.preset
+
+enable gdm.service
 enable colord.service
 enable accounts-daemon.service
 enable avahi-daemon.*</programlisting>
@@ -168,9 +171,11 @@ enable avahi-daemon.*</programlisting>
     example like the one from the first example above.</para>
 
     <example>
-      <title>Administrator policy <filename>/etc/systemd/system-preset/00-lennart.preset</filename>:</title>
+      <title>Administrator policy</title>
+
+      <programlisting># /etc/systemd/system-preset/00-lennart.preset
 
-      <programlisting>enable httpd.service
+enable httpd.service
 enable sshd.service
 enable postfix.service
 disable *</programlisting>
@@ -179,8 +184,8 @@ disable *</programlisting>
     <para>This enables three specific services and disables all
     others. This is useful for administrators to specifically select
     the units to enable, and disable all others. Due to the filename
-    prefix <literal>00-</literal> it will be read early and hence
-    overrides all other preset policy files.</para>
+    prefix <literal>00-</literal> it will be read early and
+    override all other preset policy files.</para>
   </refsect1>
 
   <refsect1>

man/tmpfiles.d.xml

@@ -697,7 +697,7 @@ d /run/uscreens 0755 root screen 10d12h
 </programlisting>
 
       <para>Contents of <filename>/run/screens</filename> and /run/uscreens will
-      cleaned up after 10 and 10½ days, respectively.</para>
+      be cleaned up after 10 and 10½ days, respectively.</para>
     </example>
 
     <example>