doc: update ui install compose to add default service

Signed-off-by: Jiyong Huang <huangjy@emqx.io>

docs/en_US/installation.md

@@ -36,6 +36,9 @@ Please make sure docker compose has installed before running.
       ports:
       - "9082:9082"
       restart: unless-stopped
+      environment: 
+        # setting default eKuiper service, works since 1.8.0
+        DEFAULT_EKUIPER_ENDPOINT: "http://ekuiper:9081"
    ekuiper:
       image: lfedge/ekuiper:x.x.x
       ports:

docs/zh_CN/installation.md

@@ -36,6 +36,9 @@ eKuiper manager 是一个免费的 eKuiper 管理控制台，以 Docker 镜像
       ports:
       - "9082:9082"
       restart: unless-stopped
+      environment: 
+        # setting default eKuiper service, works since 1.8.0
+        DEFAULT_EKUIPER_ENDPOINT: "http://ekuiper:9081"
    ekuiper:
       image: lfedge/ekuiper:x.x.x
       ports: