In particular, don't bother attempting to do substitution of the home
files and home generation derivations since these rarely, if ever,
could be substituted.
Fixes#330
This changes the installation command from
nix-shell $HM_PATH -A install --run 'home-manager switch'
to
nix-shell $HM_PATH -A install
The added shell hook will print some useful information and run
`home-manager switch`.