How to Give A Postgres User SuperUser Previllege Through docker-compose?

This is my docker-compose file section for postgres container. These settings are fine, but my django app requires this user to have superuser previlleges through this command inside postgresql.

ALTER ROLE project_admin SUPERUSER;

How can this be accomodated inside this docker-compose file?

 db:
  image: postgres:latest
  container_name: project-db
  environment:
   - POSTGRES_USER='project_admin'
   - POSTGRES_PASS='projectpass'
   - POSTGRES_DB='project'

Source: StackOverflow