Move dkim data, vmail and dbs to volumes, changed README

data/Dockerfiles/php-fpm/docker-entrypoint.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+set -e
+
+if [[ ! -d "/data/dkim/txt" || ! -d "/data/dkim/keys" ]] ; then	mkdir -p /data/dkim/{txt,keys} ; chown -R www-data:www-data /data/dkim; fi
+if [[ $(stat -c %U /data/dkim/) != "www-data" ]] ; then chown -R www-data:www-data /data/dkim ; fi
+
+exec "$@"