new line char not showing up correctly in docs

[smsaladi]

Seems to be written "correctly" in the source:

pandas/pandas/io/parsers.py

Line 251 in 4091f64

``#empty\\na,b,c\\n1,2,3`` with ``header=0`` will result in 'a,b,c' being

and parsed correctly in the .rst file:

pandas/doc/source/io.rst

Line 335 in 4091f64

For example, if ``comment='#'``, parsing '#empty\\na,b,c\\n1,2,3' with

But doesn't show up correctly in the online docs:
https://pandas.pydata.org/pandas-docs/stable/generated/pandas.read_excel.html

[vertan]

The new line problem was fixed in #18412, and the missing named argument comment is added to the read_excel documentation in the proposed PR #18753.