pre-run instructions

Sometimes we have to run WP CLI or other tools to configure instance. It would be nice to have something like this in the docker-entry
```sh
if [[ -f "/usr/local/bin/pre-run.sh" ]]; then
 /usr/local/bin/pre-run.sh
fi
ENTRYPOINT ["docker-entrypoint.sh"]
CMD ["apache2-foreground"]
```
WDYT about adding these lines into the `docker-entrypoint.sh`
