Add support for bash entrypoint

[tatemz]

Most docker containers have the ability support entering into bash by adding an entrypoint script.

Something like this will do:

entrypoint.sh

if [ "$1" == composer ]; then
  exec "composer --ansi ${@:2}"
else
  exec "$@"
fi

And in your Dockerfile

ADD entrypoint.sh /entrypoint.sh
CMD ["composer"]
ENTRYPOINT ["/entrypoint.sh"]