Makefile: Fix missing dependency of on qemu-tech.texi

The qemu-doc.{html,info,pdf,txt} depend on qemu-doc.texi and its
include files.  Except qemu-tech.texi is missing.  Has always been
missing as far as I can see.  Fix it.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Message-Id: <20190715055736.15214-2-armbru@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>

Makefile

@@ -1021,7 +1021,8 @@ pdf: qemu-doc.pdf docs/interop/qemu-qmp-ref.pdf docs/interop/qemu-ga-ref.pdf
 txt: qemu-doc.txt docs/interop/qemu-qmp-ref.txt docs/interop/qemu-ga-ref.txt
 
 qemu-doc.html qemu-doc.info qemu-doc.pdf qemu-doc.txt: \
-	qemu-img.texi qemu-nbd.texi qemu-options.texi qemu-option-trace.texi \
+	qemu-img.texi qemu-nbd.texi qemu-options.texi \
+	qemu-tech.texi qemu-option-trace.texi \
 	qemu-deprecated.texi qemu-monitor.texi qemu-img-cmds.texi qemu-ga.texi \
 	qemu-monitor-info.texi docs/qemu-block-drivers.texi \
 	docs/qemu-cpu-models.texi docs/security.texi