Remove "setup.py test" from documentation and add a CHANGELOG entry for 3.6.1

[nicoddemus]

Followup of #3536

[pytestbot]

GitMate.io thinks possibly related issues are #3538 (3.6.1 section missing from changelog), #3536 (3.6.1 fails on "setup.py test"), #582 (setup.py test documentation is broken), #1632 (Remove py.test* commands as entry points), and #592 (py.test hangs after update from 2.5 to 2.6.2).

[nicoddemus]

Actually as pointed out by #3536 (comment), we don't actually need to remove that section of the docs...

[asottile]

I assume we should remove the code as well:

pytest/setup.py

Lines 118 to 135 in 1815765

	class PyTest(Command):
	user_options = []
	def initialize_options(self):
	pass
	def finalize_options(self):
	pass
	def run(self):
	import subprocess
	python_path = [x for x in os.environ.get("PYTHONPATH", "").split(":") if x]
	python_path.insert(0, os.getcwd())
	os.environ["PYTHONPATH"] = ":".join(python_path)
	errno = subprocess.call([sys.executable, "pytest.py", "--ignore=doc"])
	raise SystemExit(errno)