Add Guix build file.

* guix.scm: New file.
* README.org (Hacking): Mention it.

.gitignore

@@ -1 +1,2 @@
 site/
+*~

README.org

@@ -21,5 +21,11 @@ haunt serve -w
 
 Now browse to http://localhost:8080/ and rejoice!
 
+Alternatively, you can build the site /via/ Guix with:
+
+#+BEGIN_SRC sh
+  guix build -f guix.scm
+#+END_SRC
+
 * License
 The sources of this website are made available to you under the Affero General Public License, either version 3 of the license or (at your option) any later version.

guix.scm

@@ -0,0 +1,45 @@
+;; -*- geiser-scheme-implementation: guile -*-
+;;; Bootstrappable.org website
+;;; Copyright © 2021 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of the Bootstrappable.org website.
+;;;
+;;; The Bootstrappable.org website is free software; you can
+;;; redistribute it and/or modify it under the terms of the Affero
+;;; General Public License as published by the Free Software
+;;; Foundation; either version 3 of the License, or (at your option)
+;;; any later version.
+;;;
+;;; The Bootstrappable.org website is distributed in the hope that it will be
+;;; useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General
+;;; Public License for more details.
+;;;
+;;; You should have received a copy of the Affero General Public
+;;; License along with these source files.  If not, see
+;;; <http://www.gnu.org/licenses/>.
+
+;;;
+;;; Run 'guix build -f guix.scm' to build the web site.
+;;;
+
+(use-modules (gnu) (guix)
+             ((guix git-download) #:select (git-predicate))
+             (gnu packages guile-xyz))
+
+(define this-directory
+  (dirname (current-filename)))
+
+(define source
+  (local-file this-directory "bootstrappable.org-checkout"
+              #:recursive? #t
+              #:select? (git-predicate this-directory)))
+
+(computed-file "bootstrappable.org"
+               (with-imported-modules '((guix build utils))
+                 #~(begin
+                     (use-modules (guix build utils))
+
+                     (copy-recursively #$source ".")
+                     (invoke #$(file-append haunt "/bin/haunt") "build")
+                     (copy-recursively "site" #$output))))