dashboard: Add Dockerfile for dashboard and update doc (#2970)

* Add dockerfile for dashboard with doc update

sentinel-dashboard/Dockerfile

@@ -0,0 +1,20 @@
+FROM amd64/buildpack-deps:buster-curl as installer
+
+ARG SENTINEL_VERSION=1.8.6
+
+RUN set -x \
+    && curl -SL --output /home/sentinel-dashboard.jar https://github.com/alibaba/Sentinel/releases/download/${SENTINEL_VERSION}/sentinel-dashboard-${SENTINEL_VERSION}.jar
+
+FROM openjdk:8-jre-slim
+
+# copy sentinel jar
+COPY --from=installer ["/home/sentinel-dashboard.jar", "/home/sentinel-dashboard.jar"]
+
+ENV JAVA_OPTS '-Dserver.port=8080 -Dcsp.sentinel.dashboard.server=localhost:8080'
+
+RUN chmod -R +x /home/sentinel-dashboard.jar
+
+EXPOSE 8080
+
+CMD java ${JAVA_OPTS} -jar /home/sentinel-dashboard.jar
+

sentinel-dashboard/README.md

@@ -58,4 +58,10 @@ java -Dserver.port=8080 \
 客户端正确配置并启动后，会**在初次调用后**主动向控制台发送心跳包，汇报自己的存在；
 控制台收到客户端心跳包之后，会在左侧导航栏中显示该客户端信息。如果控制台能够看到客户端的机器信息，则表明客户端接入成功了。
 
+## 6. 构建Docker镜像
+
+```
+docker build --build-arg SENTINEL_VERSION=1.8.6 -t ${REGISTRY}/sentinel-dashboard:v1.8.6 .
+```
+
 更多：[控制台功能介绍](./Sentinel_Dashboard_Feature.md)。