man: document automatic dependencies

For all units ensure there's an "Automatic Dependencies" section in the
man page, and explain which dependencies are automatically added in all
cases, and which ones are added on top if DefaultDependencies=yes is
set.

This is also done for systemd.exec(5), systemd.resource-control(5) and
systemd.unit(5) as these pages describe common behaviour of various unit
types.

man/systemd.scope.xml

@@ -72,6 +72,10 @@
     url="http://www.freedesktop.org/wiki/Software/systemd/ControlGroupInterface/">New
     Control Group Interfaces</ulink> for an introduction on how to make
     use of scope units from programs.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Automatic Dependencies</title>
 
     <para>Unless <varname>DefaultDependencies=false</varname>
     is used, scope units will implicitly have dependencies of
@@ -82,6 +86,11 @@
     shutdown. Only scope units involved with early boot or
     late system shutdown should disable this option.
     </para>
+
+    <para>Additional implicit dependencies may be added as result of
+    resource control parameters as documented in
+    <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
+
   </refsect1>
 
   <refsect1>