Not exactly 
You should set this variable to be the same as the arguments that you would pass to the minio gateway command. For instance, for Azure, you would set this setting to azure. The MINIO_ACCESS_KEY and MINIO_SECRET_KEY should then refer to your azurestorageaccountname and azurestorageaccountkey.
Not very intuitive, I know… If it works for you please report your findings here and I’ll update the README.