[docs] update README for routing (#12949)
[docs] update README for routing (#12949)


Co-authored-by: Juraci Paixão Kröhling <112c059aa3c53adcd644328dbabbdcbe0fa8f801@kroehling.de>
Co-authored-by: Alex Boten <1e5a92690ae5061b029620512ac8ae33d4f3a3b3@lightstep.com>
open-telemetry/opentelemetry-collector-contrib,open-telemetry/opentelemetry-collector-contrib