get-system-setting.md

## uni.getSystemSetting() @getsystemsetting

<!-- UTSAPIJSON.getSystemSetting.description -->

<!-- UTSAPIJSON.getSystemSetting.param -->

<!-- UTSAPIJSON.getSystemSetting.returnValue -->

<!-- UTSAPIJSON.getSystemSetting.example -->

<!-- UTSAPIJSON.getSystemSetting.compatibility -->

<!-- UTSAPIJSON.getSystemSetting.tutorial -->

<!-- UTSAPIJSON.get-system-setting.example -->

<!-- UTSAPIJSON.general_type.name -->

<!-- UTSAPIJSON.general_type.param -->