Improve command line help with example

[pditommaso]

This ticket aims to improve the help printed when using the --help option by adding section with usage examples.

The example should report common commands that can be used by copy & pasting them. Some examples can be found in the README file.

A good example of the format for the "Examples" section is given by kubectl;

» kubectl run -h
Create and run a particular image in a pod.

Examples:
  # Start a nginx pod
  kubectl run nginx --image=nginx

  # Start a hazelcast pod and let the container expose port 5701
  kubectl run hazelcast --image=hazelcast/hazelcast --port=5701

  # Start a hazelcast pod and set environment variables "DNS_DOMAIN=cluster" and "POD_NAMESPACE=default" in the
container
  kubectl run hazelcast --image=hazelcast/hazelcast --env="DNS_DOMAIN=cluster" --env="POD_NAMESPACE=default"

  # Start a hazelcast pod and set labels "app=hazelcast" and "env=prod" in the container
  kubectl run hazelcast --image=hazelcast/hazelcast --labels="app=hazelcast,env=prod"

  # Dry run; print the corresponding API objects without creating them
  kubectl run nginx --image=nginx --dry-run=client

  # Start a nginx pod, but overload the spec with a partial set of values parsed from JSON
  kubectl run nginx --image=nginx --overrides='{ "apiVersion": "v1", "spec": { ... } }'

  # Start a busybox pod and keep it in the foreground, don't restart it if it exits
  kubectl run -i -t busybox --image=busybox --restart=Never

  # Start the nginx pod using the default command, but use custom arguments (arg1 .. argN) for that command
  kubectl run nginx --image=nginx -- <arg1> <arg2> ... <argN>

  # Start the nginx pod using a different command and custom arguments
  kubectl run nginx --image=nginx --command -- <cmd> <arg1> ... <argN>

Options:
    --allow-missing-template-keys=true:
    If true, ignore any errors in templates when a field or map key is missing in the template. Only applies to
    golang and jsonpath output formats.

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