(Updated with minimal reproducable example) PyWake source install

Installing py_wake from source requires an additional command besides the pip install . due to git lfs. One must run python -m git_lfs post-install to start using py_wake. The least effort solution would be at least mentioning it in the docs, so users are aware of it. The most convenient option would be to run a post/pre-install script automatically (or check LFS file state on import and run the download in the background, maybe notifying user that it's going to take a bit of time for the first import), downloading those files.

@mmpe do you have any thoughts?