Add a doc to explain OTLP Trace support. (#11152)

docs/en/changes/changes.md

@@ -82,5 +82,6 @@
 * Remove `how to add menu` doc, as SkyWalking supports marketplace and new backend-based setup.
 * Separate contribution docs to a new menu structure.
 * Add a doc to explain how to manage i18n.
+* Add a doc to explain OTLP Trace support.
 
 All issues and pull requests are [here](https://github.com/apache/skywalking/milestone/181?closed=1)

docs/en/setup/backend/opentelemetry-receiver.md

@@ -1,4 +1,4 @@
-# OpenTelemetry receiver
+# OpenTelemetry Metrics Format
 
 The OpenTelemetry receiver supports ingesting agent metrics by meter-system. The OAP can load the configuration at bootstrap.
 If the new configuration is not well-formed, the OAP may fail to start up. The files are located at `$CLASSPATH/otel-rules`.
@@ -18,7 +18,7 @@ To activate the `otlp` handler and relevant rules of `istio`:
 receiver-otel:
   selector: ${SW_OTEL_RECEIVER:default}
   default:
-    enabledHandlers: ${SW_OTEL_RECEIVER_ENABLED_HANDLERS:"otlp"}
+    enabledHandlers: ${SW_OTEL_RECEIVER_ENABLED_HANDLERS:"otlp-metrics"}
     enabledOtelMetricsRules: ${SW_OTEL_RECEIVER_ENABLED_OTEL_METRICS_RULES:"istio-controlplane"}
 ```
 

docs/en/setup/backend/otlp-trace.md

@@ -0,0 +1,12 @@
+# OpenTelemetry Trace Format
+OpenTelemetry metrics and log formats are supported, the trace format is not supported directly.
+
+OpenTelemetry and Zipkin formats are generally logically consistent. 
+If the Zipkin server alternative mode is expected, user could use OpenTelemetry Collector's [Zipkin Exporter](https://opentelemetry.io/docs/specs/otel/trace/sdk_exporters/zipkin/)
+to transfer the format and forward to OAP as alternative Zipkin server.
+
+Read [Zipkin Trace Doc](zipkin-trace.md) for more details about **Zipkin Server Alternative Mode**.
+
+To contributors, if you want to contribute `otlp-trace` handler in `receiver-otel` receiver, we could accept that PR.
+But still, we could require the trace transferred into Zipkin format in the handler.
+ 

docs/en/setup/backend/zipkin-trace.md

@@ -2,6 +2,8 @@
 The Zipkin receiver makes the OAP server work as an alternative Zipkin server implementation for collecting traces. 
 It supports Zipkin v1/v2 formats through the HTTP collector and Kafka collector.
 
+**NOTICE, Zipkin trace would not be analyzed like SkyWalking native trace format.**
+
 Use the following config to activate it.
 Set `enableHttpCollector` to enable HTTP collector and `enableKafkaCollector` to enable Kafka collector.
 

docs/menu.yml

@@ -109,6 +109,8 @@ catalog:
             path: "/en/setup/backend/uninstrumented-gateways"
           - name: "Zipkin Trace"
             path: "/en/setup/backend/zipkin-trace"
+          - name: "OpenTelemetry Trace"
+            path: "/en/setup/backend/otlp-trace"
       - name: "Metrics"
         catalog:
           - name: "OAL Scripts"