ADOPTERS.md: add Yelp
ADOPTERS.md: add Yelp

Signed-off-by: Daniel Popescu <7a945665e3a00e464d0fe7af595576e359601ec9@yelp.com>

open-policy-agent/opa,tsandall/opa,tsandall/opa,tsandall/opa,open-policy-agent/opa,open-policy-agent/opa,open-policy-agent/opa,open-policy-agent/opa,tsandall/opa,open-policy-agent/opa,tsandall/opa,tsandall/opa