worker/integration: add README

Add instructions about how to run the worker/integration test suite.

Signed-off-by: Taylor Silva <tsilva@pivotal.io>

worker/integration/README.md

@@ -0,0 +1,22 @@
+## Running The `worker/integration` Test Suite
+
+This test suite only works on Linux. If you're on macOS or Windows you can use
+docker to run the Linux parts of the codebase. Use the following commands to
+run this test suite:
+
+```bash
+$ docker run -v ~/workspace/concourse:/src -it --entrypoint "/bin/bash" golang
+```
+
+The above command will put you in a terminal session inside a container with
+your local Concourse code mounted at `/src`.
+
+To run the tests:
+
+```bash
+$ cd /src/worker/integration
+$ go test
+```
+
+You can leave the container running while you modify your code. Return to the
+container whenever you want to run your tests to see if your changes work.