In my personal projects, I keep a 'package.scm' file in the root of the
source tree for use with 'guix environment -l'.  However, it's also
handy to install that package by using 'guix package -e':

    guix package -e '(primitive-load "package.scm")'

This patch adds a shorthand for this:

    guix package -f package.scm

The motivation for this is to ultimately encourage other people to keep
a 'package.scm' file in their own repos for building reproducible
development environments and easily testing development snapshots, like
what we do with our 'guix-devel' package.

I'd like to add the same option for 'guix build', if this is approved.