No instructions on activating Windows venv

[GToidZ]

ISP/assignment/ku-polls/iteration4.md

Lines 109 to 125 in 324b7a7

	### Virtual Environment
	It's a good practice to install app dependencies in a virtual environment,
	so that the packages don't modify or corrupt the system's Python installation.
	(Demo in lab.)
	Here's an example of creating a virtual env and installing dependencies.
	You can use either `python -m venv` or the `virtualenv` tool (separate package). Virtualenv claims to be faster and better, as explained on
	[StackOverflow](https://stackoverflow.com/questions/44091886/whats-the-difference-between-virtualenv-and-m-venv-in-creating-virtual-env).
	So, if you already have `virtualenv` on your system, use it.
	```
	python -m venv env # create the virtual env in "env/", only 1 time
	. env/bin/activate # start the virtual env in bash or zsh
	pip install -r requirements.txt
	```

Windows has different structure for venv, I suggest adding another code block for Windows users:

py -m venv env
.\env\Scripts\activate
pip install -r requirements.txt