Add package.json

[riaanvddool]

To allow easy install using mip:
https://docs.micropython.org/en/latest/reference/packages.html

>>> import mip
>>> mip.install('github:rguillon/schedule')
Installing github:rguillon/schedule/package.json to /lib
Copying: /lib/schedule/__init__.py
Installing ucontextlib (latest) from https://micropython.org/pi/v2 to /lib
Exists: /lib/ucontextlib.mpy
Installing logging (latest) from https://micropython.org/pi/v2 to /lib
Exists: /lib/logging.mpy
Installing time (latest) from https://micropython.org/pi/v2 to /lib
Copying: /lib/time.mpy
Done