Reference Virtual Environments Documentation, Internal or External

[pb-413]

I came to recommend adding information about environments / virtual environments, but you already have a TODO documented in your markdown.

https://github.com/pyOpenSci/python-package-guide/blob/7b422d4256cdb89d40c8b2b19227e4a5d8078817/tutorials/installable-code.md?plain=1#L502C1-L505C4

Once you decide what documentation you want to link to (internal or external), consider this issue related: https://github.com/pyOpenSci/python-package-guide/issues/254