[media] doc-rst: add media/uapi/rc/lirc-header.rst

changeset 68cd5e0b ("[media] doc-rst: add LIRC header to the book")
did everything but adding the lirc-reader.rst :-p

My fault: I forgot to do a git add for this guy on such
changeset.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/media/uapi/rc/lirc-header.rst

+.. -*- coding: utf-8; mode: rst -*-
+
+.. _lirc_header:
+
+****************
+LIRC Header File
+****************
+
+.. kernel-include:: $BUILDDIR/lirc.h.rst
+