Add reinstall dashboard warning && Update README

docs/UserGuide_en.md

@@ -5,8 +5,7 @@
 **Recommended configuration：** Prepare _two domains_ before installation，a domain can **connect to CDN** for _Public Access_，for example (status.nai.ba). Another domain name resolves to the panel server allows the Agent can connect to the Dashboard，This domain **cannot connect to CDN** You need to make it expose the ip of the panel server directly.
 
 ```shell
-curl -L https://raw.githubusercontent.com/naiba/nezha/master/script/install_en.sh  -o nezha.sh && chmod +x nezha.sh
+curl -L https://raw.githubusercontent.com/naiba/nezha/master/script/install_en.sh  -o nezha.sh && chmod +x nezha.sh && sudo ./nezha.sh
-sudo ./nezha.sh
 ```
 
 _\* Use WatchTower to automatically update the panel, and in Windows you can use nssm to configure self-start_

docs/UserGuide_zh.md

@@ -13,15 +13,13 @@
 **推荐配置：** 安装前准备 _两个域名_，一个可以 **接入 CDN** 作为 _公开访问_，比如 (status.nai.ba)；另外一个解析到面板服务器作为 Agent 连接 Dashboard 使用，**不能接入 CDN** 直接暴露面板主机 IP，比如（ip-to-dashboard.nai.ba）。
 
 ```shell
-curl -L https://raw.githubusercontent.com/naiba/nezha/master/script/install.sh  -o nezha.sh && chmod +x nezha.sh
+curl -L https://raw.githubusercontent.com/naiba/nezha/master/script/install.sh  -o nezha.sh && chmod +x nezha.sh && sudo ./nezha.sh
-sudo ./nezha.sh
 ```
 
 国内镜像加速：
 
 ```shell
-curl -L https://fastly.jsdelivr.net/gh/naiba/nezha@master/script/install.sh -o nezha.sh && chmod +x nezha.sh
+curl -L https://fastly.jsdelivr.net/gh/naiba/nezha@master/script/install.sh -o nezha.sh && chmod +x nezha.sh && sudo CN=true ./nezha.sh
-CN=true sudo ./nezha.sh
 ```
 
 _\* 使用 WatchTower 可以自动更新面板，Windows 终端可以使用 nssm 配置自启动_

script/install.sh

@@ -141,7 +141,26 @@ install_dashboard() {
     echo -e "> 安装面板"
 
     # 哪吒监控文件夹
-    mkdir -p $NZ_DASHBOARD_PATH
+    if [ ! -d "${NZ_DASHBOARD_PATH}" ]; then
+        mkdir -p $NZ_DASHBOARD_PATH
+    else
+        echo "您可能已经安装过面板端，重复安装会覆盖数据，请注意备份。"
+        read -e -r -p "是否退出安装? [Y/n] " input
+        case $input in
+        [yY][eE][sS] | [yY])
+            echo "退出安装"
+            exit 0
+            ;;
+        [nN][oO] | [nN])
+            echo "继续安装"
+            ;;
+        *)
+            echo "退出安装"
+            exit 0
+            ;;
+        esac
+    fi
+    
     chmod 777 -R $NZ_DASHBOARD_PATH
 
     command -v docker >/dev/null 2>&1
@@ -187,6 +206,9 @@ install_agent() {
     if [ ! -n "$version" ]; then
         version=$(curl -m 10 -sL "https://fastly.jsdelivr.net/gh/naiba/nezha/" | grep "option\.value" | awk -F "'" '{print $2}' | sed 's/naiba\/nezha@/v/g')
     fi
+    if [ ! -n "$version" ]; then
+        version=$(curl -m 10 -sL "https://gcore.jsdelivr.net/gh/naiba/nezha/" | grep "option\.value" | awk -F "'" '{print $2}' | sed 's/naiba\/nezha@/v/g')
+    fi
 
     if [ ! -n "$version" ]; then
         echo -e "获取版本号失败，请检查本机能否链接 https://api.github.com/repos/naiba/nezha/releases/latest"