Contributing Guide uses incorrect repo in examples

[MarkSeufert]

In the contributing guide, the instructions under the fork heading give the following git command:
git remote add upstream https://github.com/open-telemetry/opentelemetry-js.git

However, this is referring to opentelemetry-js which is the wrong repository. The git command should correctly read:
git remote add upstream https://github.com/open-telemetry/opentelemetry-js-contrib.git