Add agent compatibility doc for the first time. (#7707)

docs/en/setup/service-agent/agent-compatibility.md

@@ -0,0 +1,27 @@
+# Compatibility
+
+SkyWalking 8.0+ uses v3 protocols. Agents don't have to keep the same versions as the OAP backend.
+
+## SkyWalking Native Agents
+
+|OAP Server Version|Java|Python|NodeJS|LUA|Kong|Browser Agent|
+----------- | ---------- | --------- | --------- |--------- |--------- |--------- |
+8.0.1 - 8.1.0 | 8.0.0 - 8.3.0 | < = 0.6.0| < = 0.3.0 | All | All | No |
+8.2.0 - 8.3.0 | 8.0.0 - 8.3.0 | < = 0.6.0| < = 0.3.0 | All | All | All |
+8.4.0+ | \> = 8.0.0 | All | All | All | All | All |
+
+## Ecosystem Agents
+
+All following agent implementations are a part of SkyWalking ecosystem. All the source codes and their distributions
+don't belong to the Apache Software Foundation.
+
+|OAP Server Version|DotNet|Go2sky|cpp2sky|PHP agent|
+----------- | ---------- | --------- | --------- |--------- |
+8.0.1 - 8.3.0 | 1.0.0 - 1.3.0 | 0.4.0 - 0.6.0 | < = 0.2.0 | \> = 3.0.0|
+8.4.0+ | \> = 1.0.0 | \> = 0.4.0  | All | \> = 3.0.0|
+
+All these projects are maintained by their own communities, please reach them if you face any compatibility issue.
+
+___
+All above compatibility are only references, if you face `unimplemented` error, it means you need to upgrade OAP backend
+to support newer features in the agents.

docs/menu.yml

@@ -61,6 +61,8 @@ catalog:
         path: "/en/setup/service-agent/server-agents"
       - name: "Browser Agent"
         path: "/en/setup/service-agent/browser-agent"
+      - name: "Compatibility"
+        path: "/en/setup/service-agent/agent-compatibility"
       - name: "Backend"
         catalog:
           - name: "Quick Start"