add more build/run info in README

README.md

@@ -3,6 +3,8 @@
 prometheus docker build
 
 ## build 
+`docker-compose build`
+or
 ```{bash}
 GO_VERSION=1.16.0 # optional
 PROMETHEUS_VERSION=2.25.0 # optional, will use latest available, if unset
@@ -11,4 +13,11 @@ docker \
     --build-arg GO_VERSION="${GO_VERSION}" \
     --build-arg PROMETHEUS_VERSION="${PROMETHEUS_VERSION}" \
     -t prometheus:"${PROMETHEUS_VERSION}"-local .
-```
+```
+
+## run
+use the provided `docker-compose.yml`:
+`docker-compose up -d`
+the container assumes a systemd-enabled system and logs to journald.
+using `docker logs prometheus` or `docker-compose logs` still works, though.
+