增加一条FAQ

docs/en/faq.md

@@ -47,6 +47,10 @@
 
     The ESP32 has 34 GPIO pins, of which GPIO 34-39 is only used as an input and cannot be used as an output. Others can be used as both an input and an output pin.
 
+- **Q7: Why does the Stick with MPU9250 burn the factory firmware and press button A, the result shows "No", which means "No 9250"?**
+
+    Restart this Stick and then it can display correctly. Because the code to read the MPU9250 is placed in the setup() function which only was executed once when booting. So reboot and let the Stick detect MPU9250 again.
+
 ## Unit
 
 - **Q1: What is the difference between the various cameras of M5Stack?**

docs/zh_CN/faq.md

@@ -48,6 +48,10 @@
 
     ESP32 有 34 个 GPIO 管脚，其中 GPIO 34-39 仅用作输入，不能作为输出，其他的既可以作为输入又可以作为输出管脚。
 
+- **Q7: 为什么带 MPU9250 的 Stick 烧录了出厂固件之后，按按键 A，结果显示 "No"，即 "不存在9250"。**
+
+    重启这个 Stick，就可以显示。因为读取 MPU9250 的代码放置在出厂程序的 setup() 函数中，开机只执行一次，所以重启，让 Stick 再检测一次 MPU9250。
+
 ## 单元
 
 - **Q1: M5Stack 的多款摄像头 Unit 之间有什么区别？**