[docs/contributing] OpenTelemetry Contributor Guide link is broken

[emdneto]

In https://opentelemetry.io/docs/contributing/, the link here for the OpenTelemetry Contributor Guide is broken:

For guidance on how to contribute to the OpenTelemetry project in general, see the OpenTelemetry Contributor Guide , which provides details on the Contributor License Agreement and the Code of Conduct. Every language implementation, Collector, and conventions repository has its own specific contributing guides.

Fix that by using the link: https://github.com/open-telemetry/community/blob/main/guides/contributor/README.md