Add new benchmark tutorial

[matsvanmolle]

It is not intuitive to make your own campaign from scratch. A good step-by-step tutorial should be provided for new users.

[apaolillo]

@matsvanmolle What do you have in mind? Besides what we have in tutorials/

[matsvanmolle]

@apaolillo The tutorials in tutorial/ are good for running your first campaign and getting results. There is in my opinion no tutorial that guides you in creating your first benchmark and campaign. For example a tutorial could be to benchmark a simple pthread program. If you want to I could create a PR in my spare time to illustrate what I mean.

[apaolillo]

I think you can go ahead an propose a tutorial, now that you know benchkit quite well 😃