Error and resolution when following Phoenix setup instructions

phoenix-setup-mix.create

# after 'brew install postgres' and starting the service 'brew services start postgresql' to get rid of error:
# "FATAL 28000 (invalid_authorization_specification): role "postgres" does not exist"

psql -d template1
CREATE ROLE postgres LOGIN CREATEDB PASSWORD 'postgres';

# exit psql and run mix.create to set up the dev server