Update readme with SERVICE environment variable support
## First Setup
-To push your build target to a docker registry you first need to change the default target, replace `SERVICE` variable in the makefile to your docker registry
+To push your build target to a docker registry you first need to change the default target, export `SERVICE` environment variable to your docker registry
+
+```shell script
+export SERVICE=<registry>/<image-name>:<tag>
+```
For the first build of the build container run:
`skipper build bm-inventory-build`
