Have you read the description on Docker Hub? You always should start with that:
Docker Hub: postgres
POSTGRES_HOST_AUTH_METHOD set to
trust. It is actually in the container logs when you start it without a non-empty password.
Error: Database is uninitialized and superuser password is not specified.
You must specify POSTGRES_PASSWORD to a non-empty value for the
superuser. For example, "-e POSTGRES_PASSWORD=password" on "docker run".
You may also use "POSTGRES_HOST_AUTH_METHOD=trust" to allow all
connections without a password. This is *not* recommended.
See PostgreSQL documentation about "trust":
So you have to things you should always do. Reading the README/documentation and checking logs.