Virtual Environments with pip

[PaSchue]

Description

Add a section about virtual environments to content/python/concepts/pip/pip.md. Virtual environments and pip go hand in hand, which is why it makes sense to give a short introduction on how to use venv with pip.

My contribution includes the following:

• Best practices
• Setting up a venv
• Generating a requirements.txt

Type of Change

• Editing an existing entry (fixing a typo, bug, issues, etc)

Checklist

• All writings are my own.
• My entry follows the Codecademy Docs style guide.
• My changes generate no new warnings.
• I have performed a self-review of my own writing and code.
• I have checked my entry and corrected any misspellings.
• I have made corresponding changes to the documentation if needed.
• I have confirmed my changes are not being pushed from my forked main branch.
• I have confirmed that I'm pushing from a new branch named after the changes I'm making.
• I have linked any issues that are relevant to this PR in the Issues Solved section.

[CLAassistant]

All committers have signed the CLA.