DOC: read_excel() documentation for na_values should show default na values
I'd like to see read_excel show the same valid information for na_values as read_csv does. This ended up taking a lot of digging to find because it was unclear what the defaults were with read_excel().
#### read_csv() documentation shows the following for na_values

na_values : str or list-like or dict, default None
Additional strings to recognize as NA/NaN. If dict passed, specific per-column NA values. By default the following values are interpreted as NaN: ‘’, ‘#N/A’, ‘#N/A N/A’, ‘#NA’, ‘-1.#IND’, ‘-1.#QNAN’, ‘-NaN’, ‘-nan’, ‘1.#IND’, ‘1.#QNAN’, ‘N/A’, ‘NA’, ‘NULL’, ‘NaN’, ‘nan’.
#### read_excel() documentation does not include default NaN values

na_values : list-like, default None
List of additional strings to recognize as NA/NaN
