Add Docker image doc (#6780)

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

+# Docker
+
+This section introduces how to build your Java application image on top of this image.
+
+```dockerfile
+FROM apache/skywalking-java-agent:8.5.0-jdk8
+
+# ... build your java application
+```
+
+You can start your Java application with `CMD` or `ENTRYPOINT`, but you don't need to care about the Java options to
+enable SkyWalking agent, it should be adopted automatically.
+
+# Kubernetes
+
+This section introduces how to use this image as sidecar of Kubernetes service.
+
+In Kubernetes scenarios, you can also use this agent image as a sidecar.
+
+```yaml
+apiVersion: v1
+kind: Pod
+metadata:
+  name: agent-as-sidecar
+spec:
+  restartPolicy: Never
+
+  volumes:
+    - name: skywalking-agent
+      emptyDir: { }
+
+  containers:
+    - name: agent-container
+      image: apache/skywalking-java-agent:8.4.0-alpine
+      volumeMounts:
+        - name: skywalking-agent
+          mountPath: /agent
+      command: [ "/bin/sh" ]
+      args: [ "-c", "cp -R /skywalking/agent /agent/" ]
+
+    - name: app-container
+      image: springio/gs-spring-boot-docker
+      volumeMounts:
+        - name: skywalking-agent
+          mountPath: /skywalking
+      env:
+        - name: JAVA_TOOL_OPTIONS
+          value: "-javaagent:/skywalking/agent/skywalking-agent.jar"
+```
+

docs/menu.yml

@@ -61,6 +61,10 @@ catalog:
         catalog:
         - name: "Setup"
           path: "/en/setup/service-agent/java-agent/readme"
+        - name: "Setup in Docker"
+          path: "/en/setup/service-agent/java-agent/containerization#docker"
+        - name: "Setup in Kubernetes"
+          path: "/en/setup/service-agent/java-agent/containerization#kubernetes"
         - name: "Supported middleware, framework and library"
           path: "/en/setup/service-agent/java-agent/Supported-list"
         - name: "Agent Configuration Properties"