Documentation: add multi-threading notes

[Youw]

need add notes to README regarding multithreading, e.g. regarding Windows issues/non-full support
maybe some more

[Youw]

NOTE for everyone: hidapi not thread-safe in general, with a few platform-specific/usage-spacific exceptions.

Damn, I need to get my hands to describe everything in details.

[mcuee]

Reference: Windows: unable to interrupt blocking hid_read call #133