Add documentation about track contributing documentation

[kytrinyx]

add file: /language-tracks/documentation/for-contributors.md

Talk about:

• track readme
• contributing guide
• pull request / issue templates

[masters3d]

Where is the info about UUID?

[kytrinyx]

It's in the language tracks documentation (https://github.com/exercism/docs/tree/master/language-tracks) under configuration > exercises: https://github.com/exercism/docs/blob/master/language-tracks/configuration/exercises.md

[masters3d]

@kytrinyx Can I add a link of those files to the readme.md? Or would that break the website?

[kytrinyx]

Let's wait until we get #100 sorted out—we should probably have several things linked in the README.