add notes

Author: Guillaume Revaillot

README.md

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 Java based library to talk to stm32 UART bootloader following [AN3155](https://www.st.com/resource/en/application_note/cd00264342.pdf)
 
 See [stm32flash-util](https://github.com/grevaillot/stm32flash-util) for usage.
+
+## Notes:
+
+  - Project has not been tested against much devices.
+  - Device table is taken from [stm32flash](https://sourceforge.net/projects/stm32flash/) project.