documentation is incomplete

[TomasTomecek]

• [x] how to use section -- code listings are incomplete
• [x] please don't use terms standalone container, rather present it as a demo
• [x] make sure the proper image, which is available on github on our modularitycontainers namespace, is used everywhere...
• [x] ...and there is an example command how to obtain the image

For more info, check my PR against haproxy: https://github.com/container-images/haproxy/pull/4