esp32/README: Add hint about using GNUmakefile on case-insensitive FS.
esp32/README: Add hint about using GNUmakefile on case-insensitive FS.

Peetz0r/micropython-esp32,micropython/micropython-esp32,micropython/micropython-esp32,MrSurly/micropython-esp32,MrSurly/micropython-esp32,micropython/micropython-esp32,Peetz0r/micropython-esp32,Peetz0r/micropython-esp32,MrSurly/micropython-esp32,SHA2017-badge/micropython-esp32,SHA2017-badge/micropython-esp32,Peetz0r/micropython-esp32,SHA2017-badge/micropython-esp32,SHA2017-badge/micropython-esp32,MrSurly/micropython-esp32,MrSurly/micropython-esp32,micropython/micropython-esp32,SHA2017-badge/micropython-esp32,Peetz0r/micropython-esp32,micropython/micropython-esp32