Added documentation on USE_CPP_FILE option for blinky example

README.md

@@ -32,7 +32,7 @@ It uses cmake and GCC, along with newlib (libc), STM32Cube. Supports F0 F1 F2 F3
 * `blinky` ([examples/blinky](examples/blinky)) - blink led using STM32 HAL library and SysTick.
    It will compile a project for the `F4` family by default, but you can also compile for the
    `L0` and `F1` family by passing `BLINKY_L0_EXAMPLE=ON` or `BLINKY_F1_EXAMPLE=ON` to the CMake
-   generation call.
+   generation call. Using C++ instead of C is possible using `USE_CPP_FILE=ON`.
 * `freertos` ([examples/freertos](examples/freertos)) - blink led using STM32 HAL library and FreeRTOS.
    You need to specify at least one board by passing `FREERTOS_<BOARD>_EXAMPLE=ON` to CMake.
    Currently, the example can be built for the `H743ZI` and `F407VG` board targets.