parse-headers.rst: add an introduction to the man page

The pod2rst tool generated a man page for parse-headers.pl
script, but it is better to put it into some context.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
1 file changed