correct baseimage info README

Author: sparklyballs

README.md

@@ -47,7 +47,7 @@ http://192.168.x.x:8080 would show you what's running INSIDE the container on po
 * `-e PUID` for UserID - see below for explanation
 * `-e TZ` for setting timezone information, eg Europe/London
 
-It is based on phusion-baseimage with ssh removed, for shell access whilst the container is running do `docker exec -it piwigo /bin/bash`.
+It is based on alpine linux with s6 overlay, for shell access whilst the container is running do `docker exec -it piwigo /bin/bash`.
 
 ### User / Group Identifiers