Update README.md

Author: amiller

dstack-database/README.md

@@ -9,7 +9,7 @@ To start this exploration, here's a minimal fault-tolerant database service usin
 It's a docker-compose simulation environment for 3 nodes.
 You can crash/pause any 1 of them, and the other 2 will make progress.
 
-- `./Dockerfile` starts from postgres base image
+- `./Dockerfile` starts from ubuntu, mainly installs postgres patroni and zookeeper
 - `./docker-compose.yml` defines three services
 - `./patroni.yml` configures the postgres
 - `./start.sh` runs zookeeper, fixes directory permissions, runs patroni