Add a comment at the beginning of example files & README.txt

It would have help me to find a little comment into the examples files to understand more quickly how to use it, so here it is.

I had to read the specification.txt for that, which is not bad but it would have been far more natural if its content had been displayed in the main page of GitHub
=> this is why I renamed it to README.txt

What do you think of all this ?