scripts: home: Make ‘guix home import’ write home-configuration.scm.

* guix/scripts/home.scm (process-command): Populate ‘home-configuration.scm’
  in the destination directory instead of printing to stdout.
* doc/guix.texi (Declaring the Home Environment): Adjust accordingly.
(Invoking guix home): Likewise.

Suggested-by: Ludovic Courtès <ludo@gnu.org>
Co-authored-by: Ludovic Courtès <ludo@gnu.org>

doc/guix.texi

@@ -35933,9 +35933,8 @@ The @command{guix home import} command reads some of the ``dot files''
 such as @file{~/.bashrc} found in your home directory and copies them to
 the given directory, @file{~/src/guix-config} in this case; it also
 reads the contents of your profile, @file{~/.guix-profile}, and, based
-on that, it outputs a Home configuration that resembles your current
+on that, it populates @file{~/src/guix-config/home-configuration.scm}
-configuration.  You can dump that configuration to a file and you're
+with a Home configuration that resembles your current configuration.
-ready to go!
 
 A simple setup can include Bash and a custom text configuration, like in
 the example below.  Don't be afraid to declare home environment parts,
@@ -36667,33 +36666,14 @@ $ guix home list-generations 10d
 @item import
 Generate a @dfn{home environment} from the packages in the default
 profile and configuration files found in the user's home directory.  The
-configuration files will be copied to the specified directory.  Note
+configuration files will be copied to the specified directory, and a
-that not every home service that exists is supported (@pxref{Home
+@file{home-configuration.scm} will be populated with the home
-Services}).
+environment.  Note that not every home service that exists is supported
+(@pxref{Home Services}).
 
 @example
 $ guix home import ~/guix-config
-;; This "home-environment" file can be passed to 'guix home reconfigure'
+guix home: '/home/alice/guix-config' populated with all the Home configuration files
-;; to reproduce the content of your profile.  This is "symbolic": it only
-;; specifies package names.  To reproduce the exact same profile, you also
-;; need to capture the channels being used, as returned by "guix describe".
-;; See the "Replicating Guix" section in the manual.
-
-(use-modules
-  (gnu home)
-  (gnu packages)
-  (gnu home services shells))
-
-(home-environment
-  (packages
-    (map specification->package
-         (list "glibc-locales" "nss-certs" "nss")))
-  (services
-    (list (service
-            home-bash-service-type
-            (home-bash-configuration
-              (bashrc
-                (list (local-file "/home/charlie/guix-config/.bashrc"))))))))
 @end example
 
 @end table

guix/scripts/home.scm

@@ -274,7 +274,15 @@ argument list and OPTS is the option alist."
                            (_ (leave (G_ "wrong number of arguments~%"))))))
        (unless (file-exists? destination)
          (mkdir-p destination))
-       (import-manifest manifest destination (current-output-port))))
+       (call-with-output-file
+           (string-append destination "/home-configuration.scm")
+         (cut import-manifest manifest destination <>))
+       (info (G_ "'~a' populated with all the Home configuration files~%")
+             destination)
+       (display-hint (format #f (G_ "\
+Run @command{guix home reconfigure ~a/home-configuration.scm} to effectively
+deploy the home environment described by these files.\n")
+                             destination))))
     ((describe)
      (match (generation-number %guix-home)
        (0