add a reference to the Chef code of conduct
add a reference to the Chef code of conduct

Link to the Chef Community Guidelines.

Signed-off-by: Robb Kidd <11cd4f9ba93acb67080ee4dad8d03929f9e64bf2@chef.io>

nellshamrell/supermarket,robbkidd/supermarket,chef/supermarket,robbkidd/supermarket,robbkidd/supermarket,chef/supermarket,chef/supermarket,juliandunn/supermarket,nellshamrell/supermarket,juliandunn/supermarket,chef/supermarket,nellshamrell/supermarket,juliandunn/supermarket,nellshamrell/supermarket,robbkidd/supermarket,chef/supermarket,juliandunn/supermarket