README is missing cross-compile instructions

[sai-y]

Earlier, there used to be an instruction in README on how to cross compile python files from the command line. Especially, this line:

python -m mpy_cross -mno-unicode -msmall-int-bits=31 filename.py

It would be great if this line weren't removed from the Readme. I bring it up because it is important to include information related to including your own library for application development. The current information in Readme seems to be related to a plugin.

[tomlogic]

And it needs to mention that the mpy_cross version matters. See this forum posting for details:

https://www.digi.com/support/forum/70255/how-to-cross-compile-micropython-code-for-xbee3