Add test info

README.md

 functions for retrieving the higher-level data structures (such as containers
 and labels) that the reporter service creates.
 
+## Tests [![CircleCI](https://circleci.com/gh/csmith/docker-service-reporter-lib.svg?style=svg)](https://circleci.com/gh/csmith/docker-service-reporter-lib)
+
+A separate Dockerfile for tests is located in the tests directory. It depends
+on a 'dev' label of csmith/service-reporter-lib. You can build and run the
+tests like so:
+
+```
+docker build -t csmith/service-reporter-lib:dev .
+docker build -t csmith/service-reporter-lib-test:dev test
+docker run --rm -it csmith/service-reporter-lib-test:dev
+```
+