Update some doc. (#5942)

* Update manual-sdk.md

* Update README.md

* Update README.md

docs/en/concepts-and-designs/manual-sdk.md

 # Manual instrument SDK
 We have manual instrument SDK contributed from the community.
 - [Go2Sky](https://github.com/SkyAPM/go2sky). Go SDK follows SkyWalking format.
-
-Welcome to consider contributing in following languages:
-- Python
-- C++
+- [C++](https://github.com/SkyAPM/cpp2sky). C++ SDK follows SkyWalking format. 
 
 ## What is SkyWalking formats and propagation protocols?
 See these protocols in [protocols document](../protocols/README.md).
 
-## Can SkyWalking provide OpenCensus exporter in above languages?
-At the moment I am writing this document, **NO**. Because, OC(OpenCensus) don't support context extendable 
-mechanism, and no hook mechanism when manipulate spans. SkyWalking relied on those to propagate more things
-than trace id and span id.
-
-We are already in the middle of discussion, see https://github.com/census-instrumentation/opencensus-specs/issues/70.
-After OC provides this officially, we can.
-
-## How about Zipkin instrument SDKs?
-See [Zipkin receiver](../setup/backend/backend-receivers.md) in backend **Choose receiver** section. 
+## Envoy tracer
+Envoy has its internal tracer implementation for SkyWalking. Read [SkyWalking Tracer doc](https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/trace/v3/skywalking.proto.html?highlight=skywalking) and [SkyWalking tracing sandbox](https://www.envoyproxy.io/docs/envoy/latest/start/sandboxes/skywalking_tracing.html?highlight=skywalking) for more details.

docs/en/setup/README.md

@@ -27,9 +27,11 @@ You can go to their project repositories for additional info about guides and re
 
 - [SkyAPM Node.js agent](https://github.com/SkyAPM/SkyAPM-nodejs). See Node.js server side agent project document for more details.
 
-- [SkyAPM PHP SDK](https://github.com/SkyAPM/SkyAPM-php-sdk). See PHP agent project document for more details.
+- [SkyAPM PHP agent](https://github.com/SkyAPM/SkyAPM-php-sdk). See PHP agent project document for more details.
 
-- [SkyAPM GO2Sky](https://github.com/SkyAPM/go2sky). See GO2Sky project document for more details.
+- [SkyAPM Go SDK](https://github.com/SkyAPM/go2sky). See go2sky project document for more details.
+
+- [SkyAPM C++ SDK](https://github.com/SkyAPM/cpp2sky). See cpp2sky project document for more details.
 
 ## Browser Monitoring
 [Apache SkyWalking Client JS](https://github.com/apache/skywalking-client-js). Support collecting metrics and error logs