Update README with usage

README.md

@@ -4,6 +4,33 @@ Runs a once-off ECS task and streams the output via Cloudwatch Logs.
 
 ## Usage
 
+```
+NAME:
+   ecs-run-task - run a once-off task on ECS and tail the output from cloudwatch
+
+USAGE:
+   ecs-run-task [options] [command override]
+
+COMMANDS:
+     help, h  Shows a list of commands or help for one command
+
+GLOBAL OPTIONS:
+   --debug                        Show debugging information
+   --file value, -f value         Task definition file in JSON or YAML
+   --name value, -n value         Task name
+   --cluster value, -c value      ECS cluster name (default: "default")
+   --log-group value, -l value    Cloudwatch Log Group Name to write logs to (default: "ecs-task-runner")
+   --service value, -s value      service to replace cmd for
+   --fargate                      Specified if task is to be run under FARGATE as opposed to EC2
+   --security-group value         Security groups to launch task in (required for FARGATE). Can be specified multiple times
+   --subnet value                 Subnet to launch task in (required for FARGATE). Can be specified multiple times
+   --env KEY=value, -e KEY=value  An environment variable to add in the form KEY=value or `KEY` (shorthand for `KEY=$KEY` to pass through an env var from the current host). Can be specified multiple times
+   --help, -h                     show help
+   --version, -v                  print the version
+```
+
+### Example
+
 ```bash
 $ aws-vault exec myprofile -- ecs-run-task --file examples/helloworld/taskdefinition.json echo "Hello from Docker!"
 
@@ -13,7 +40,7 @@ Hello from Docker!
 
 ## Development
 
-We're using Go 1.11 with GO111MODULE=on.
+We're using Go 1.11 with [modules](https://github.com/golang/go/wiki/Modules).
 
 ```bash
 export GO111MODULE=on