Add component library settings document back.

docs/en/setup/backend/Component-library-settings.md

@@ -0,0 +1,61 @@
+# Component library settings
+Component library settings are about your own or 3rd part libraries used in monitored application.
+
+In agent or SDK, no matter library name collected as ID or String(literally, e.g. SpringMVC), collector
+formats data in ID for better performance and less storage requirements. 
+
+Also, collector conjectures the remote service based on the component library, such as: 
+the component library is MySQL Driver library, then the remote service should be MySQL Server. 
+
+For those two reasons, collector require two parts of settings in this file:
+1. Component Library id, name and languages.
+1. Remote server mapping, based on local library.
+
+**All component names and IDs must be defined in this file.**
+
+## Component Library id
+Define all component libraries' names and IDs, used in monitored application.
+This is a both-way mapping, agent or SDK could use the value(ID) to represent the component name in uplink data.
+
+- Name: the component name used in agent and UI
+- id: Unique ID. All IDs are reserved, once it is released.
+- languages: Program languages may use this component. Multi languages should be separated by `,`
+
+### ID rules
+- Java and multi languages shared: (0, 3000]
+- .NET Platform reserved: (3000, 4000]
+- Node.js Platform reserved: (4000, 5000]
+- Go reserved: (5000, 6000]
+- PHP reserved: (6000, 7000]
+
+Example
+```yaml
+Tomcat:
+  id: 1
+  languages: Java
+HttpClient:
+  id: 2
+  languages: Java,C#,Node.js
+Dubbo:
+  id: 3
+  languages: Java
+H2:
+  id: 4
+  languages: Java
+```
+
+## Remote server mapping
+Remote server will be conjectured by the local component. The mappings are based on Component library names.
+
+- Key: client component library name
+- Value: server component name
+
+```yaml
+Component-Server-Mappings:
+  Jedis: Redis
+  StackExchange.Redis: Redis
+  SqlClient: SqlServer
+  Npgsql: PostgreSQL
+  MySqlConnector: Mysql
+  EntityFrameworkCore.InMemory: InMemoryDatabase
+```

docs/en/setup/service-agent/java-agent/Plugin-Development-Guide.md

@@ -157,10 +157,8 @@ SpanLayer is the catalog of span. Here are 5 values:
 1. HTTP
 1. MQ
 
-Component IDs are defined and protected by SkyWalking project, 0 -> 10000 IDs are reserved. If you want to contribute
-a new plugin, you can ask for an official ID, after your pull request approved and automatic test cases accepted by PMC.
-Please use > 10000 ID, if you are going to develop a private plugin or don't intend to contribute the plugin to community,
-to avoid the ID conflict.
+Component IDs are defined and reserved by SkyWalking project.
+For component name/ID extension, please follow [component library setting document](../../backend/Component-library-settings.md).
 
 ## Develop a plugin
 ### Abstract

docs/en/setup/service-agent/java-agent/README.md

@@ -67,6 +67,10 @@ Now, we have the following known plugins.
     * If you want to use annotations or SkyWalking native APIs to read context, try [SkyWalking manual APIs](Application-toolkit-trace.md)
     * If you want to continue traces across thread manually, use [across thread solution APIs](Application-toolkit-trace-cross-thread.md).
 
+## Plugin Development Guide
+SkyWalking java agent supports plugin to extend [the supported list](Supported-list.md). Please follow 
+our [Plugin Development Guide](Plugin-Development-Guide.md).
+
 # Test
 If you are interested in plugin compatible tests or agent performance, see the following reports.
 * [Plugin Test](https://github.com/SkywalkingTest/agent-integration-test-report)