readme: update sections on environment variables
readme: update sections on environment variables

ory/hydra,ory/hydra,ory/hydra,Grillz/hydra,Bridg/hydra-1,ory/hydra,ory-am/hydra,ory-am/go-iam,ory-am/go-iam,Bridg/hydra-1,Grillz/hydra,Bridg/hydra-1,leetal/hydra