docs: list/description of standard PyHyper 'words'

[pbeaucage]

PyHyper standardizes certain dimension names such as energy, polarization, sam_x, sam_th, but we have no centralized repository of these names. This would be a great documentation page.

[pbeaucage]

This is in the PyHyper manuscript which has lived on my desk for the last... embarrassing amount of time:

timestamp/epoch should be added and explained... and this should be a docs page.