Doc: signal.sig(timed)wait do not work outside the main thread

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-01-25.17:25:31.331>
labels = ['3.11', 'type-feature', 'docs']
title = 'Doc: signal.sig(timed)wait do not work outside the main thread'
updated_at = <Date 2021-10-22.10:01:01.554>
user = 'https://github.com/petr-motejlek'

bugs.python.org fields:

activity = <Date 2021-10-22.10:01:01.554>
actor = 'iritkatriel'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2017-01-25.17:25:31.331>
creator = 'petr@motejlek.net'
dependencies = []
files = []
hgrepos = []
issue_num = 29374
keywords = []
message_count = 2.0
messages = ['286269', '286284']
nosy_count = 3.0
nosy_names = ['docs@python', 'martin.panter', 'petr@motejlek.net']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue29374'
versions = ['Python 3.11']