[subinterpreters] Confusing docs about state after calling Py_NewInterpreter()

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-08-19.19:05:22.486>
labels = ['expert-subinterpreters']
title = '[subinterpreters] Confusing docs about state after calling Py_NewInterpreter()'
updated_at = <Date 2020-05-15.00:53:42.586>
user = 'https://github.com/nanjekyejoannah'

bugs.python.org fields:

activity = <Date 2020-05-15.00:53:42.586>
actor = 'vstinner'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Subinterpreters']
creation = <Date 2019-08-19.19:05:22.486>
creator = 'nanjekyejoannah'
dependencies = []
files = []
hgrepos = []
issue_num = 37888
keywords = []
message_count = 1.0
messages = ['349964']
nosy_count = 2.0
nosy_names = ['eric.snow', 'nanjekyejoannah']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue37888'
versions = []