Recommend pipx for installation

[clbarnes]

pipx is an excellent tool which converts PyPI into a package repository without the concern of clashing dependencies etc., by managing individual virtual environments for every application installed by pipx (and their dependencies). Console scripts are symlinked into the user's $PATH, just like pip install --user. This keeps the tool installed at the user level, rather than tied to any particular project's virtual environment, while keeping it out of the system/ user root python environment.