man: fix typo in the alias symlink name

Symlink created by Alias will use the value as the file name.

man/systemd.unit.xml

@@ -173,13 +173,13 @@
     section. When the unit is enabled, symlinks will be created for those names, and removed when the unit is
     disabled. For example, <filename>reboot.target</filename> specifies
     <varname>Alias=ctrl-alt-del.target</varname>, so when enabled, the symlink
-    <filename>/etc/systemd/system/ctrl-alt-del.service</filename> pointing to the
+    <filename>/etc/systemd/system/ctrl-alt-del.target</filename> pointing to the
     <filename>reboot.target</filename> file will be created, and when
     <keycombo><keycap>Ctrl</keycap><keycap>Alt</keycap><keycap>Del</keycap></keycombo> is invoked,
-    <command>systemd</command> will look for the <filename>ctrl-alt-del.service</filename> and execute
-    <filename>reboot.service</filename>. <command>systemd</command> does not look at the [Install] section at
-    all during normal operation, so any directives in that section only have an effect through the symlinks
-    created during enablement.</para>
+    <command>systemd</command> will look for <filename>ctrl-alt-del.target</filename>, follow the symlink to
+    <filename>reboot.target</filename>, and execute <filename>reboot.service</filename> as part of that target.
+    <command>systemd</command> does not look at the [Install] section at all during normal operation, so any
+    directives in that section only have an effect through the symlinks created during enablement.</para>
 
     <para>Along with a unit file <filename>foo.service</filename>, the directory
     <filename>foo.service.wants/</filename> may exist. All unit files symlinked from such a directory are