Clarify that the (...) convertor to PyArg_ParseTuple... accepts any sequence.

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-02-01.09:03:29.813>
labels = ['docs']
title = 'Clarify that the (...) convertor to PyArg_ParseTuple... accepts any sequence.'
updated_at = <Date 2019-02-14.16:59:26.001>
user = 'https://github.com/anntzer'

bugs.python.org fields:

activity = <Date 2019-02-14.16:59:26.001>
actor = 'serhiy.storchaka'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2019-02-01.09:03:29.813>
creator = 'Antony.Lee'
dependencies = []
files = []
hgrepos = []
issue_num = 35874
keywords = []
message_count = 2.0
messages = ['334660', '335546']
nosy_count = 3.0
nosy_names = ['docs@python', 'serhiy.storchaka', 'Antony.Lee']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue35874'
versions = []