README: add basic instructions for adding new devices
README: add basic instructions for adding new devices

This is for the best case where it's just about adding a new device ID. In the
case where reverse engineering is required, some more detailed instructions
are necessary but they take more effort to write...

Signed-off-by: Peter Hutterer <b9c50af7afa7642f6f854434cda9ffe54ece8b85@who-t.net>

whot/libratbag,libratbag/libratbag,cvuchener/libratbag,NoXPhasma/libratbag,cvuchener/libratbag,NoXPhasma/libratbag,libratbag/libratbag,whot/libratbag,cvuchener/libratbag,whot/libratbag,libratbag/libratbag,NoXPhasma/libratbag