Clarifies that producer and consumer span do not share a critical path (#36)
Clarifies that producer and consumer span do not share a critical path (#36)

Clarifies some bits around critical path coming from a discussion with @KyleU

For example, producer spans indicate an asynchronous boundary, so children of that should not be interpreted as contributing to the critical path of the caller.
openzipkin/zipkin-api,openzipkin/zipkin-api