Update the README with development documentation
Update the README with development documentation

Signed-off-by: Chris Boertien <b01b3caad11baf20609e5b876fd52518d8a2ccb6@bz-labs.com>

jspizziri/spree_volume_pricing,solidusio-contrib/solidus_volume_pricing,jspizziri/spree_volume_pricing,solidusio-contrib/solidus_volume_pricing,jspizziri/spree_volume_pricing,redglory/spree_volume_pricing,redglory/spree_volume_pricing,spree-contrib/spree_volume_pricing,spree-contrib/spree_volume_pricing,solidusio-contrib/solidus_volume_pricing,redglory/spree_volume_pricing,solidusio-contrib/solidus_volume_pricing,spree-contrib/spree_volume_pricing