Contributing link is dead

[fed135]

Bug description

Newcomers to the project are given a bad link to the contribution guidelines pages.

What is the current behavior?

Clicking the link from https://github.com/yarnpkg/yarn/blob/master/CONTRIBUTING.md leads to a 404 page.

What is the expected behavior?

The link should lead to a functioning page.

Steps to Reproduce

1. Follow the link to https://yarnpkg.com/org/contributing
2. Observe it returns a 404

Environment

N/A

[merceyz]

Fixed in 0a121f6