guix-package: Create ~/.guix-profile when it doesn't exist.

* guix-package.in (guix-package): Create the %USER-ENVIRONMENT-DIRECTORY
  symlink if it doesn't exist yet.
* doc/guix.texi (Invoking guix-package): Document it.

doc/guix.texi

@@ -428,6 +428,12 @@ the transaction.  Upon completion, a new profile is created, but
 previous generations of the profile remain available, should the user
 want to roll back.
 
+For each user, a symlink to the user's default profile is automatically
+created in @file{$HOME/.guix-profile}.  This symlink always point to the
+current generation of the user's default profile.  Thus, users can add
+@file{$HOME/.guix-profile/bin} to their @code{PATH} environment
+variable, and so on.
+
 @table @code
 
 @item --install=@var{package}

guix-package.in

@@ -458,6 +458,13 @@ Install, remove, or upgrade PACKAGES in a single transaction.\n"))
   (setvbuf (current-error-port) _IOLBF)
 
   (let ((opts (parse-options)))
+
+    ;; Create ~/.guix-profile if it doesn't exist yet.
+    (when (and %user-environment-directory
+               %current-profile
+               (not (file-exists? %user-environment-directory)))
+      (symlink %current-profile %user-environment-directory))
+
     (with-error-handling
       (or (process-query opts)
           (parameterize ((%guile-for-build
@@ -466,7 +473,3 @@ Install, remove, or upgrade PACKAGES in a single transaction.\n"))
                                                   %bootstrap-guile
                                                   guile-final))))
             (process-actions opts))))))
-
-;; Local Variables:
-;; eval: (put 'guard 'scheme-indent-function 1)
-;; End: