Update README.md with image instructions

Updates README.md to inform how to run with the goliothiot/xk6-coap
image.

Signed-off-by: Daniel Mangum <georgedanielmangum@gmail.com>

README.md

@@ -6,6 +6,25 @@
 
 ## Getting Started
 
+To get started, either build the `k6` binary or use the
+[`goliothiot/xk6-coap`](https://hub.docker.com/repository/docker/goliothiot/xk6-coap)
+image.
+
+### Using the OCI Image
+
+The quickest way to get started is by using the `goliothiot/xk6-coap` image,
+which is [built](./images/xk6-coap/Dockerfile) from this repository and
+published to DockerHub. Tests can be supplied when creating a container from the
+image via a [bind mount](https://docs.docker.com/storage/bind-mounts/). For
+example, the following command would run the [simple
+example](./examples/simple.js) from this repository.
+
+```
+docker run -it --rm -v $(pwd)/examples/simple.js:/simple.js goliothiot/xk6-coap k6 run /simple.js --vus 10 --duration 5s
+```
+
+### Building a k6 Binary
+
 Using `k6` extentions requires including the extension(s) in a `k6` build. The
 [`xk6`](https://github.com/grafana/xk6) tool will handle executing the build,
 and the `Makefile` in this repository will ensure that `xk6` is installed and