from_clipboard doesn't work by default when copying string cells from excel
need to do `pd.read_clipboard(sep='\t')` and then things work fine.
Since it's for interactive use, it should be ok to change the default
without breaking existing code.

we did the same to `to_clipboard()` in #5070, I missed the fact that
`read_clipboard` only works out of the box for pure numerical data right now.

Why don't users report this stuff I don't know.
