Update README.md (#12)

Author: murphm8

README.md

@@ -1,7 +1,28 @@
 ## AWS Robomaker Bundle Support Library
 
+**This API is currently under active development and should not be considered stable.**
+
 A Library in Go that supports download and extraction of colcon-bundle format. https://github.com/colcon/colcon-bundle
 
+## CLI
+
+We provide a rudimentary CLI to expose the base functionality of this library. 
+With `GOMODULE11=on` you can run it by executing:
+
+`go run github.com/aws-robotics/aws-robomaker-bundle-support-library/cmd/cli`
+
+Usage:
+
+```
+./cli --bundle my_bundle.tar
+
+--bundle - Path to bundle file
+--prefix - Prefix to put onto the source command. This is generally used when the CLI is run
+on a host, but the source command will run inside a Docker container. If you have your cache 
+directory mounted as '/cache' in the Docker container you should set prefix to '/cache'.
+
+```
+
 ## License
 
 This library is licensed under the Apache 2.0 License.