Update get-app-base-info.md

docs/api/get-app-base-info.md

@@ -8,6 +8,8 @@
 
 <!-- UTSAPIJSON.getAppBaseInfo.returnValue -->
 
+- appTheme如取值为`auto`，代表跟随系统。此时需通过[getSystemInfo](./get-system-info.md)或[getDeviceInfo](./get-device-info.md)查询osTheme获取当前到底是light还是dark。
+
 <!-- UTSAPIJSON.getAppBaseInfo.example -->
 
 <!-- UTSAPIJSON.getAppBaseInfo.tutorial -->