Get more examples to understand better how to use the library

[francoisthire]

It would be nice to have more examples on how to use the library, in particular with traces. Some interface files are not always present and it requires to read the source code to understand what functions are doing.

More precisely:

• It would be nice if the example in the README, it would be nice to understand what each instruction is doing
• It seems the example is not up to date with the last version:

Ambient_context.with_storage_provider 

does not exist.

[c-cube]

I don't have much time right now to write docs, so contribs would be welcome. I can answer questions though (discord or irc) :)