Request: adding Docker health check to postgres/README.md #2391

It would be good to add a healthcheck to the postgres/README.md.

There are some possible starting points posed here: https://stackoverflow.com/questions/65115627/safe-ways-to-specify-postgres-parameters-for-healthchecks-in-docker-compose

Aside: running the below:

---
version: "3.8"
services:
    postgres:
        image: postgres:latest
        environment:
            POSTGRES_USER: user
            POSTGRES_PASSWORD: pass
            POSTGRES_DB: db

docker compose up postgres --detach 
docker compose run postgres pg_isready --username user --dbname db

I can never get pg_isready to output something besides /var/run/postgresql:5432 - no response