I create an Dockerfile with Postgresql with this code:

```
FROM postgres:9.4
MAINTAINER Fabio Ebner
ENV POSTGRES_PASSWORD="dna44100"
ENV POSTGRES_PORT=5432
EXPOSE ${POSTGRES_PORT}
COPY init.sql /docker-entrypoint-initdb.d/

```

so How can I specify to always save my db data in my user Machine? cause with this code everty time I stop the container my data are lost