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

data/Dockerfiles/dovecot/docker-entrypoint.sh

@@ -3,4 +3,6 @@ set -e
 
 sed -i "/^connect/c\connect = \"host=mysql dbname=${DBNAME} user=${DBUSER} password=${DBPASS}\"" /etc/dovecot/sql/*
 
+if [[ $(stat -c %U /var/vmail/) != "vmail" ]] ; then chown -R vmail:vmail /var/vmail ; fi
+
 exec "$@"