bluepill boards - upload_protocol = serial is supported but not documented

[lnlp]

See: https://docs.platformio.org/en/latest/boards/ststm32/bluepill_f103c8_128k.html#uploading https://docs.platformio.org/en/latest/boards/ststm32/bluepill_f103c8.html#uploading

Uploading

BluePill F103C8 (128k) supports the next uploading protocols:

blackmagic cmsis-dap dfu jlink stlink Default protocol is stlink

You can change upload protocol using upload_protocol option:

Upload protocol serial is supported but not documented. The documentation should be updated.