Add helpful information to the SETUP.md

[kytrinyx]

The contents of the SETUP.md file gets included in
the README.md that gets delivered when a user runs the exercism fetch
command from their terminal.

At the very minimum, it should contain a link to the relevant
language-specific documentation on
help.exercism.io.

It would also be useful to explain in a generic way how to run the tests.
Remember that this file will be included with all the problems, so it gets
confusing if we refer to specific problems or files.

Some languages have very particular needs in terms of the solution: nested
directories, specific files, etc. If this is the case here, then it would be
useful to explain what is expected.

---

Thanks, @tejasbubane for suggesting that we add this documentation everywhere.
See exercism.io#2198.

[pminten]

This is hard to do at the moment since we're not sure yet how the tests will run in the future (i.e. whether cargo will be involved or not).

[andrewclarkson]

I just submitted another PR (#26) to get all the examples working with Cargo.
If everybody likes the way that works out, I could write the setup file and some README's which would:

1. Point to the Rust install page (all versions should come with cargo)
2. Telling the user that once they create a file they can cd into a exercise directory and run cargo test to compile and run all the tests.

The question is should we follow the Nightly or Beta channel?

[kytrinyx]

Yeah, it's better to hold off until that has been resolved.

[EduardoBautista]

@bitborn We would only have to recommend Nightly or Beta until May 15th, which is when 1.0.0 is planned to ship.

[EduardoBautista]

I don't really understand where exactly the SETUP.md file is included.

[kytrinyx]

When the README for each exercise is assembled, it takes:

• The name of the exercise (based on the directory name for the problem)
• The shared description from $PROBLEM.md from x-common https://github.com/exercism/x-common)
• The contents of SETUP.md
• The source information from $PROBLEM.yml

[EduardoBautista]

In that order I assume?

[EduardoBautista]

Here it is: #28

[pminten]

Yup, looks great.