DOC: pd.read_csv doc-string clarification

[jreback]

need to update the docs for read_csv to match the doc-string. Let's make sure they have the same text / examples as much as possible (and are in the same order and such).

In particular, the header option doesn't have header='infer' which is the default in the docs, but it exists in the doc-string.

Further, should show what this does:

       if kwds.get('header', 'infer') == 'infer':
            kwds['header'] = 0 if kwds.get('names') is None else None

meaning if the the header kw is not specified, this it is set to the first line if no names are specified, else None.