add descriptions of some options in uproot.open

[tomeichlersmith]

While working on updating the documentation for coffea (scikit-hep/coffea#1615) I saw a few options that were undocumented, so I'm adding a few lines of documentation to them based off my understanding of the code (mostly other docstrings already existing within uproot).

[tomeichlersmith]

Thanks @ariostas , I'll get to the last few broader comments this afternoon

[tomeichlersmith]

Alright, I realized that instead of copying the same text everywhere, we can ..include it to make it easier to update in the future. I can drop the ..include and manually copy the same descriptions everywhere if you prefer.