kafka spancollector documentation update

Fix documentation on how spans are transferred to Kafka.

brave-spancollector-kafka/README.md

@@ -2,8 +2,7 @@
 
 SpanCollector that is used to submit spans to Kafka.
 
-Spans are sent to kafka as keyed messages: the key is the topic `zipkin` 
-and the value is a TBinaryProtocol encoded Span.
+Spans are sent to a topic named `zipkin` and contain no key or partition only a value which is a TBinaryProtocol encoded Span.
 
 ## Monitoring ##
 
@@ -13,4 +12,4 @@ counters in your metrics tool. When a span gets dropped, the reason is written t
 The number of spans sent to the target collector can be calculated by subtracting the dropped count from the accepted count.
 
 Refer to `DropwizardMetricsSpanCollectorMetricsHandlerExample` for an example of how to integrate with
-[dropwizard metrics](https://github.com/dropwizard/metrics).
+[dropwizard metrics](https://github.com/dropwizard/metrics).