venv `--help` docs don't specify the exact activation command

[JosephSBoyle]

Proposal

Add the commands to activate venv on the current platform to the help text displayed when printing python -m venv --help

Pitch

Many people who work cross-platform and use venv will forget the activation commands on one or both platforms.
For me, this means I have to google the command whenever I'm working on Windows.

The current --help text related to activating the venv is:

Once an environment has been created, you may wish to activate it, e.g. by sourcing an activate script in its bin directory

My thoughts are we could add the activation command somewhere beneath this text.

[sobolevn]

There are MULTIPLE ways to activate a venv. It includes: your os, your shell, your path. Maybe something else.

I think it is better to keep this as-is.

[JosephSBoyle]

If people are using the CLI (which I assume they are in this example, to even see the --help text) then I also imagine that they would want to use the shell method?

[sobolevn]

Which one?

» tree .venv/bin
.venv/bin
├── Activate.ps1
├── activate
├── activate.csh
├── activate.fish

[JosephSBoyle]

The one for their current shell, if that can be inferred reliably, or all of them, if it cannot