ci: add github action

.github/workflows/build.yml

@@ -0,0 +1,19 @@
+name: Build examples
+on:
+  push:
+    branches:
+    - master
+  pull_request:
+
+jobs:
+  build-release-v4_4:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout repo
+      uses: actions/checkout@v2
+      with:
+        submodules: 'recursive'
+    - name: esp-idf build
+      uses: espressif/esp-idf-ci-action@release-v4.4
+      with:
+        path: 'examples/factory_demo'

README.md

@@ -2,6 +2,8 @@
 
 # ESP-BOX AIoT Development Framework
 
+[![Build examples](https://github.com/espressif/esp-box/actions/workflows/build.yml/badge.svg)](https://github.com/espressif/esp-box/actions/workflows/build.yml)
+
 **Important Note:**
 
 > We recommend [updating the application firmware](./docs/firmware_update.md) when you first receive the product to have the new features and bugfix. Click [here](./docs/getting_started.md) to access the user guide of the latest release firmware. Click [here](https://github.com/espressif/esp-box/releases) to visit the older firmware.

README_cn.md

@@ -3,6 +3,8 @@
 
 # ESP-BOX AIoT 开发框架
 
+[![Build examples](https://github.com/espressif/esp-box/actions/workflows/build.yml/badge.svg)](https://github.com/espressif/esp-box/actions/workflows/build.yml)
+
 **重要提醒：**
 > 我们建议您在第一次收到产品时[更新应用固件](./docs/firmware_update_cn.md)以获得最新功能和 bug 的修复，点此[链接](./docs/getting_started_cn.md)获取应用固件的使用说明。点击[此处](https://github.com/espressif/esp-box/releases)查看历史固件。