$ sudo pkg install -y py36-websockify
...

$ websockify -?
Traceback (most recent call last):
  File "/usr/local/bin/websockify", line 6, in <module>
    from pkg_resources import load_entry_point
  File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 3250, in <module>
    @_call_aside
  File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 3234, in _call_aside
    f(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 3263, in _initialize_master_working_set
    working_set = WorkingSet._build_master()
  File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 583, in _build_master
    ws.require(__requires__)
  File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 900, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 786, in resolve
    raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'numpy' distribution was not found and is required by websockify

$ uname -KUpr
12.0-STABLE amd64 1200512 1200512

$ sudo pkg install -y py36-numpy
...

$ websockify -?
Usage: 
    websockify [options] [source_addr:]source_port [target_addr:target_port]
    websockify [options] [source_addr:]source_port -- WRAP_COMMAND_LINE

websockify: error: no such option: -?