Clarification needed: not clear which of the samples work on which existing USD implementations

[hybridherbst]

The question has come up a couple times in the working group -
I think part of what makes this repo useful is giving people wanting to use USD as interchange format an understanding of what different applications support. So I think readme files of the various subfolders could note if/what of that works in systems, and then users or implementers can amend that / correct it / extend it with screenshots or notes. This helps to form an understanding of problems to look out for both when implementing USD and when authoring assets that aim for cross-compatibility.

For me in particular, understanding which schemas / features / combinations thereof are supported in AR QuickLook and in Omniverse. For some sample assets (#4, #5, #6, #8), I added minimal info / screenshots on that, which I think would be a start for other readme's as well.

[erich666]

Related issue: #32 - is there a "gold standard" for viewing animation, for example? USDView doesn't do it well for the Elephant, for example. It will play the animation, but you must first zoom way out first in order to see it, unclipped. The iPhone shows this model fine on load, no adjustment needed.