feat: update _episodes/01-environment.md (single file)

[hollandjg]

• Add an overview section at the top which outlines all the key points of the lesson
• Add some extra material on installing packages with pip and applications with pipx
• Update section on task runners
• Include a section on using alternative backends for task runners

Resolves:

• Update _episodes/01-environment.md #12

[henryiii]

This isn't exactly true; conda uses libmamba by default now, and should be pretty close to the same speed as mamba. There shouldn't be that much reason to use mamba over conda now. micromamba, on the other hand, is a pure C++ rewrite, and is a bit faster than conda with libmamba or mamba, and is a single binary that doesn't need to bootstrap Python, so maybe just swapping "mamba" for "micromamba" would make this more accurate.