* Fix venv command examples
The documentation refers to `venv`, which is native to Python3.
However, the command examples are as if they were still `virtualenv`,
which is a package independent of `venv`:
- It doesn't need to be installed via `pip`. In fact `pip install venv` would
return an error.
- The correct way to invoke `venv` is `python3 -m venv`, not `venv`, which would
return command not found.
See https://docs.python.org/3/library/venv.html
I suspect the documentation simply replaced all occurrences of `virtualenv` with
`venv`. However they are different modules and are used differently.
* Update comment [ci skip]
Xiang Ji