Write down development notes

[szszszsz]

Write down development notes, describing how to test done changes, setup USB/IP, where to find tests, etc.

• possible problems with the environment setup
• setting the simulation up and running
• pytest's test execution from pynitrokey

Connected: #93 (comment)

[robin-nitrokey]

Ideally we’d have a docs/usbip.md in the nitrokey-3-firmware repository that describes how to setup the usbip runner. To debug an application, you would then only have to patch the runner to use a local dependency for that application.