lzma documentation: example to XZ compress file on disk

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-11-28.20:41:15.049>
labels = ['3.8', 'type-feature', '3.7', 'expert-IO', 'docs']
title = 'lzma documentation: example to XZ compress file on disk'
updated_at = <Date 2017-11-28.20:50:25.989>
user = 'https://github.com/dhimmel'

bugs.python.org fields:

activity = <Date 2017-11-28.20:50:25.989>
actor = 'dhimmel'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation', 'IO']
creation = <Date 2017-11-28.20:41:15.049>
creator = 'dhimmel'
dependencies = []
files = []
hgrepos = []
issue_num = 32160
keywords = []
message_count = 2.0
messages = ['307163', '307166']
nosy_count = 2.0
nosy_names = ['docs@python', 'dhimmel']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue32160'
versions = ['Python 3.7', 'Python 3.8']