build: mention -march in pkg-config description

build: mention -march in pkg-config description

Applications need to at least match DPDK's -march option to build
successfully due to some static inline functions in the public headers.

This might cause problems, especially in distributions, so add a note
in the pkg-config description.

Fixes: a25a650be5f0 ("build: add infrastructure for meson and ninja builds")
Cc: stable@dpdk.org
Signed-off-by: Luca Boccassi <bluca@debian.org>
Reviewed-by: Gavin Hu <gavin.hu@arm.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>