docs: Add conda-forge install instructions

[matthewfeickert]

Resolves #83

• Add install instructions from conda-forge for pixi and conda.
• Add conda-forge badge.

[matthewfeickert]

@arturbekasov this is ready for review.

[arturbekasov]

Why is this preferable to the more common ‘pip install’?

[matthewfeickert]

This pattern is the only way to make sure that the pip you want is the pip you get, as even in a virtual environment it is possible to mess up paths and get a pip elsewhere which is not the pip tied to the python that created the environment. It is also the recommended pattern by the pip and Python docs. Example: https://docs.python.org/3/installing/index.html