Expand example documentation (#2570)

## Motivation and Context

The current README for the example services is fairly spartan.

## Description

I've expanded the README, specifically:

- Clean up some markup
- Document pre-reqs.
- Document all make targets.
- Avoid the $BINARY because it looks like a bash variable.
- Expand intro

## Testing
<!--- Please describe in detail how you tested your changes -->
<!--- Include details of your testing environment, and the tests you ran
to -->
<!--- see how your change affects other areas of the code, etc. -->

n/a

## Checklist

n/a

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Co-authored-by: Matteo Bigoi <1781140+crisidev@users.noreply.github.com>
Co-authored-by: david-perez <d@vidp.dev>