docs: Update HACKING

To tell libvirt-{qemu,lxc}.h shouldn't be included either.

HACKING

@@ -786,9 +786,12 @@ stick to the following general plan for all *.c source files:
   {
       ...
 
-Of particular note: *Do not* include libvirt/libvirt.h or libvirt/virterror.h.
-It is included by "internal.h" already and there are some special reasons why
-you cannot include these files explicitly.
+Of particular note: *Do not* include libvirt/libvirt.h, libvirt/virterror.h,
+libvirt/libvirt-qemu.h, or libvirt/libvirt-lxc.h. They are included by
+"internal.h" already and there are some special reasons why you cannot include
+these files explicitly. One of the special cases, "libvirt/libvirt.h" is
+included prior to "internal.h" in "remote_protocol.x", to avoid exposing
+*_LAST enum elements.
 
 
 Printf-style functions

docs/hacking.html.in

@@ -929,10 +929,12 @@
 </pre>
 
     <p>
-      Of particular note: <b>Do not</b> include libvirt/libvirt.h or
-      libvirt/virterror.h.  It is included by "internal.h" already and there
-      are some special reasons why you cannot include these files
-      explicitly.
+      Of particular note: <b>Do not</b> include libvirt/libvirt.h,
+      libvirt/virterror.h, libvirt/libvirt-qemu.h, or libvirt/libvirt-lxc.h.
+      They are included by "internal.h" already and there are some special reasons
+      why you cannot include these files explicitly. One of the special cases,
+      "libvirt/libvirt.h" is included prior to "internal.h" in "remote_protocol.x",
+      to avoid exposing *_LAST enum elements.
     </p>