ENH: add support for reading binary Excel files (#15914)
Hi, this is a quick fix for #15914.

After reading the issue I'm not sure if this is meant to be supported though, please let me know!

I ran into this issue when trying to pass to `read_excel` a binary file downloaded with `requests` so I think it would make sense to support this natively without the user having to figure out the need to call `io.BytesIO` first. If so, do we need to update other docstrings?

Thank you!

- [x] closes #15914
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Thank you @gfyoung, I have updated the `read_excel` docstring Thanks @ftruzzi! Thank you @gfyoung @simonjayhawkins @WillAyd for your help and thorough reviews! Happy to contribute :)