man: add a new section for EFI variables

We should probably refer to them from other man pages
for programs which use them, since right now all refs are
in systemd-boot(7). But creating the section is a good step
anyway.

tools/make-directive-index.py

@@ -52,6 +52,16 @@ TEMPLATE = '''\
                 <variablelist id='environment-variables' />
         </refsect1>
 
+        <refsect1>
+                <title>EFI variables</title>
+
+                <para>EFI variables understood by
+                <citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+                and other programs.</para>
+
+                <variablelist id='efi-variables' />
+        </refsect1>
+
         <refsect1>
                 <title>UDEV directives</title>