Updated raw_pose_processing, README, and .gitignore

[icedwater]

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Dear Eric, thanks for sharing this dataset.

I've suggested a few changes that I feel might be useful - ignoring binary archives and media files will make reviewing git changes easier... and I've also tweaked the info in the raw_pose_processing notebook to give more detail about the sub-datasets.

Sorry about the metadata changes in the notebook, I forgot to clean them up.