stm32/mboot: Update README to describe WB and littlefs support.
stm32/mboot: Update README to describe WB and littlefs support.

Signed-off-by: Damien George <99e6b749acbfbe2a596df99e91d24d6e1fdbee00@micropython.org>

selste/micropython,henriknelson/micropython,selste/micropython,bvernoux/micropython,pramasoul/micropython,henriknelson/micropython,adafruit/circuitpython,henriknelson/micropython,kerneltask/micropython,adafruit/circuitpython,kerneltask/micropython,kerneltask/micropython,adafruit/circuitpython,MrSurly/micropython,pramasoul/micropython,henriknelson/micropython,bvernoux/micropython,MrSurly/micropython,selste/micropython,selste/micropython,pramasoul/micropython,kerneltask/micropython,henriknelson/micropython,kerneltask/micropython,bvernoux/micropython,MrSurly/micropython,bvernoux/micropython,selste/micropython,bvernoux/micropython,adafruit/circuitpython,pramasoul/micropython,adafruit/circuitpython,adafruit/circuitpython,MrSurly/micropython,MrSurly/micropython,pramasoul/micropython