Propose to distribute a user-only install script, not admin required

[Josh Marshall]

Hello all,

One thing which I think could significantly aid adoption would be up
either add an option or add a new installer script with guix
configured to install and run purely out of the user's home directory
without any special permissions.  Conceptually, guix shouldn't need to
have any elevated permissions given it is acceptable to use resources
less efficiently when they are in contention.  This would also allow
guix to be a drop in replacement to tools which already allow
individual users to install and use them without a hassle, like
Anaconda.

I'm not sure what all of the work required for this would be, or if it
is already in the long term plan.