Clarify default hdf5 compression python-interop

[ilan-gold]

Since 8db0474 the default compression has been ztsd, which requires the hdf5plugin in python. This isn't great for interop with python as it requires people to figure this fact out and the error message you get when it isn't installed/imported isn't super helpful. At the minimum cutting a release with ebcdb99#diff-c2a34a7f4367f08e38a028b2ef6c41076aeaa697f32d0c9bfe417edffbfc8f49R39-R41 released would allow ArcInstitute/cyto#219 to move forward with a bit more confidence, but also could be good to document on the README.

Thanks!