doc: add installing from FreeBSD package
doc: add installing from FreeBSD package

Update the FreeBSD GSG to cover installing from the pre-built package as
well as installing from a port.

Also, since the port is now based on meson, update the instructions for
compiling and running the example applications.

Signed-off-by: Bruce Richardson <66b9e8e8fbd5e9f41f91b0af050876182ce9d0e4@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk