Add sample program to the repository

[rdragos]

In the readme it is mentioned how input_data and test_func are used but I cannot see an example of these files. I think it would be useful to have some samples inside the repository.

[kitschysynq]

We could add a reference to the readme but samples are available in github.com/capeprivacy/functions

[rdragos]

I found out about the functions repo from @yanndupis on a private channel, just saying that it would be nice to have some reference in a getting started document.