Fix links to "sibling" .md files

[lynxnake]

So that they will open ok from github

[ee7]

The links are designed to work on the website (here, https://exercism.org/docs/building/tooling/test-runners - where the links do work). It's expected that they don't work on GitHub. I know it's confusing - sorry.

From the README.md in this repo:

Please note that these docs are meant to be read at https://exercism.org/docs - not in this website. Links in this repository are relative to the website, not internally in this repo.

@ErikSchierboom I think we'll keep running into this problem. What do you think about pinning an issue in this repo to make the situation more visible?

Previously: #158 (comment), #162, #163, #230, #234, #243, #312, #350, #351, #360, #386

[lynxnake]

Thanks, closing it

[ErikSchierboom]

What do you think about pinning an issue in this repo to make the situation more visible?

That sounds like a good idea.

[ee7]

That sounds like a good idea.

I've created #397.