add binary install commandos

[ruben-arts]

closes #70

[traversaro]

Thanks @ruben-arts !

[ruben-arts]

@wolfv What would be a nice replacement for the Macos version?

[wolfv]

I think we could install into ~/.pixi/ and tell the user to add it to the PATH (since they'd need it anyways for the shims?

[traversaro]

Not sure if this belongs to this PR, but it could make sense to also document how to uninstall pixi from the system once it has been installed using the documented steps?

[ruben-arts]

This is now completely rewritten into an install script for the systems that can easily be fetched using a web get a tool like curl.

To test it use on linux:

curl -fsSL https://raw.githubusercontent.com/prefix-dev/pixi/docs/add_binary_install_command/scripts/install.sh | bash

or on windows:

iwr -useb https://raw.githubusercontent.com/prefix-dev/pixi/docs/add_binary_install_command/scripts/install.ps1 | iex

[ruben-arts]

@traversaro Added a small section for the uninstall

[traversaro]

Thanks!