Update document.

docs/en/concepts-and-designs/README.md

@@ -19,7 +19,5 @@ SkyWalking already support.
   - [Overview](backend-overview.md). Provides a high level introduction about the OAP backend.
   - [Observability Analysis Language](oal.md). Introduces the core languages, which is designed for aggregation behaviour definition.
   - [Query in OAP](query-oap.md). Introduces how to query data from backend, whether a simple metric data or topology map, even trace or log.
-  - [Receiver for other tracers](trace-receiver.md). Helps you to know the purposes of receiving other libs(such as Zipkin, Jeager, OpenCensus) data. 
-Also how to process this kind of data format.
 - UI
   - [Overview](ui-overview.md).

docs/en/concepts-and-designs/backend-overview.md

@@ -23,6 +23,9 @@ even for Zipkin data format. The AOP analysis the segments to get metrics, and p
 the streaming aggregation.
 1. Consider tracing as some kinds of logging only. Just provide save and visualization capabilities for trace. 
 
+Also, SkyWalking accepts trace formats from other project, such as Zipkin, Jeager, OpenCensus.
+These formats could be processed in the two ways too.
+
 ## Metric in OAP
 Metric in OAP is totally new feature in 6 series. Build observability for a distributed system based on metric of connected nodes.
 No tracing data is required.