add docs/app-push-fcm.md.

docs/app-push-fcm.md

+#### 准备条件  
+
+- 可访问Google服务器  
+注意：中国境内无法访问Google服务器
+- 注册Google账号  
+- 了解什么是 `Firebase Cloud Messaging`,确定你是否需要用它
+  + [介绍](https://firebase.google.com/docs/cloud-messaging)
+  + [Android设置文档](https://firebase.google.com/docs/cloud-messaging/android/client)
+  + [iOS设置文档](https://firebase.google.com/docs/cloud-messaging/ios/client)
+
+
+#### 申请开通FCM  
+
+1. 打开[Firebase引导页](https://firebase.google.com)  
+
+2. 创建新项目  
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_project_setup_1.jpg)  
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_project_setup_2.jpg)  
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_project_setup_3.jpg)  
+
+3. 创建`iOS`平台配置  
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_project_setup_1.jpg)
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_project_setup_2.jpg)
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_project_setup_3.jpg)
+将 `GoogleService-Info.plist` 下载到本地，HBuilderX中云端打包需要使用此文件  
+
+4. 创建`Android`平台配置 (如已创建项目，无须创建新项目，直接进行Android平台的配置)  
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_project_setup_1.jpg)  
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_project_setup_2.jpg)  
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_project_setup_3.jpg)  
+项目创建完成后，进入项目配置Android平台的包名、签名证书步骤如下：
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_android_setup_start.png)  
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_android_setup_package.png)  
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_android_setup_download_config_file.png)
+将 `google-services.json` 下载到本地，HBuilderX中云端打包需要使用此文件  
+
+
+#### iOS平台FCM后台推送消息  
+
+1. 上传APNS证书  
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_ios_upload_profile.jpg)
+
+2. 网页端实现推送客户端功能  
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_create_notification_1.jpg)
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_create_notification_2.jpg)
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_create_notification_3.jpg)
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_create_notification_4.jpg)
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_create_notification_5.jpg)
+
+
+####  Android平台FCM后台推送消息  
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_create_notification_1.jpg)
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_create_notification_2.jpg)
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_create_notification_3.jpg)
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_create_notification_4.jpg)
+![](https://native-res.dcloud.net.cn/images/uniapp/push/firebase/firebase_create_notification_5.jpg)
+