Build Dockerfile with e.g.:
$ docker build -t wamos .

Get a running instance with e.g.:
$ docker run --name wamos -d -p 54321:5432 wamos

Create ER diagram with e.g.:
$ postgresql_autodoc -p 54321 -h $dockerhost \
      -U wamos --password=wamos -t dot
$ dot -Tpng wamos.dot > wamos.png