docs: Inform new developers about other related repos (#575)
docs: Inform new developers about other related repos (#575)

This is the main OpenTelemetry Python repo, but now we have another one (and possibly more in the future) for related instrumentation-related code.

Explain this in the contributing instructions to inform new developers about the existence of this repo so that they are aware of this and they efforts can be directed to the right place.
open-telemetry/opentelemetry-python,open-telemetry/opentelemetry-python