Modify according to code review comments

Signed-off-by: surechen <chenshuo17@huawei.com>

docs/skywalking/skywalking.md

@@ -1,52 +1,36 @@
 # SkyWalking
 
-Skywalking-manager is a handler plugin of mesher, it reports tracing data to skywalking server
+Skywalking-manager is a handler plugin of mesher, it reports tracing data to skywalking server.
 
 ## Configurations
 **In conf/mesher.conf**
 
 **servicecomb.apm.tracing.enable**
->  *(optional, bool)* enable apm
+>  *(optional, bool)* enable application performance manager
 
 **servicecomb.apm.tracing.serverUri**
 >  *(optional, string)* server address of skywalking
 
 ## Example
 ```yaml
 servicecomb:
-  apm:
+  apm:                              #application performance monitor
     tracing:
-      enable: true
-      serverUri: 127.0.0.1:11800
+      enable: true                  #enable tracing ability
+      serverUri: 127.0.0.1:11800    #url of skywalking 
 ```
+## Step：
 
-## SkyWawlking-Manager Init
-**In file proxy/bootstrap/bootstrap.go**
-```shell script
-import "github.com/apache/servicecomb-mesher/proxy/pkg/skywalking"
-```
-**In function Start()**
-```shell script
-skywalking.Init()
-```
-
-**In function SetHandlers() add two Handlers**
-```shell script
-consumerChain := strings.Join([]string{
-		...
-		skywalking.SkyWalkingConsumer,
-		chassisHandler.Transport,
-}}
+# 1. SkyWawlking-Manager Init
+**You must init skywawlking manager pkg which will manage connection and report msg to skywalking**
+- For example:
+- [1] You can import skywalking manager proxy/pkg/skywalking in file proxy/bootstrap/bootstrap.go.
+- [2] Calling function Init() in proxy/pkg/skywalking manually to init skywalking manager.
+- [3] Adding skywalking's consumer handler name SkyWalkingConsumer defined in proxy/pkg/skywalking to consumerChain.
+- [4] Adding skywalking's provider handler name SkyWalkingProvider defined in proxy/pkg/skywalking to providerChain.
+- more details about handler chains in [go-chassis](https://github.com/go-chassis/go-chassis#readme)
 
-providerChain := strings.Join([]string{
-		...
-		skywalking.SkyWalkingProvider,
-		chassisHandler.Transport,
-}}
+# 2. SkyWalking-Handler Init
+- You must import proxy/handler pkg to init skywalking handler. Not only skywalking handler, all the handlers which are customized for mesher are defined here.
+- For example you can import handler pkg in file cmd/mesher/mesher.go
 
-```
-## SkyWalking-Handler Init
-**In cmd/mesher/mesher.go**
-```shell script
-import _ "github.com/apache/servicecomb-mesher/proxy/handler"
-```

proxy/config/struct.go

@@ -74,12 +74,12 @@ type Tracing struct {
 	ServerURI string `yaml:"serverUri"`
 }
 
-//Apm is for Application Performance Management
-type Apm struct {
+//APM is for Application Performance Management
+type APM struct {
 	Tracing Tracing `yaml:"tracing"`
 }
 
 //ServiceComb is for servicecomb config
 type ServiceComb struct {
-	APM Apm `yaml:"apm"`
+	APM APM `yaml:"apm"`
 }

proxy/handler/skywalking_handler.go

@@ -32,8 +32,9 @@ const (
 )
 
 const (
-	HTTPClientComponentID = 2
-	HTTPServerComponentID = 49
+	HTTPClientComponentID  = 2
+	ServiceCombComponentID = 28
+	HTTPServerComponentID  = 49
 )
 
 //SkyWalkingProviderHandler struct

proxy/handler/skywalking_handler_test.go

@@ -44,7 +44,7 @@ func initGcConfig() {
 
 //initMesherConfig
 func initMesherConfig() {
-	config.SetConfig(&config.MesherConfig{ServiceComb: &config.ServiceComb{config.Apm{config.Tracing{Enable: true, ServerURI: "192.168.0.1:17289"}}}})
+	config.SetConfig(&config.MesherConfig{ServiceComb: &config.ServiceComb{config.APM{config.Tracing{Enable: true, ServerURI: "192.168.0.1:17289"}}}})
 }
 
 //initInv

proxy/pkg/skywalking/skywalking_manager_test.go

@@ -42,7 +42,7 @@ func initConfig() {
 
 //initMesherConfig
 func initMesherConfig() {
-	config.SetConfig(&config.MesherConfig{ServiceComb: &config.ServiceComb{config.Apm{config.Tracing{Enable: true, ServerURI: "192.168.0.1:17289"}}}})
+	config.SetConfig(&config.MesherConfig{ServiceComb: &config.ServiceComb{config.APM{config.Tracing{Enable: true, ServerURI: "192.168.0.1:17289"}}}})
 }
 
 //initInv