Add docs about Embedding with an frozen module limitation.

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-12-17.20:09:34.639>
labels = ['3.7', '3.8', 'docs']
title = 'Add docs about Embedding with an frozen module limitation.'
updated_at = <Date 2017-12-17.20:09:59.825>
user = 'https://github.com/AraHaan'

bugs.python.org fields:

activity = <Date 2017-12-17.20:09:59.825>
actor = 'Decorater'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2017-12-17.20:09:34.639>
creator = 'Decorater'
dependencies = []
files = []
hgrepos = []
issue_num = 32353
keywords = ['patch']
message_count = 1.0
messages = ['308497']
nosy_count = 2.0
nosy_names = ['docs@python', 'Decorater']
pr_nums = ['4910']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue32353'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']