gnu: bs1770gain: Adjust the usage text and home-page.

* gnu/packages/audio.scm (bs1770gain)[source]: Add snippet.
[home-page]: Update.

gnu/packages/audio.scm

@@ -19,6 +19,7 @@
 ;;; Copyright © 2018 Eric Bavier <bavier@member.fsf.org>
 ;;; Copyright © 2018 Brendan Tildesley <brendan.tildesley@openmailbox.org>
 ;;; Copyright © 2019 Pierre Langlois <pierre.langlois@gmx.com>
+;;; Copyright © 2019 Leo Famulari <leo@famulari.name>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -3215,11 +3216,20 @@ (define-public bs1770gain
                            version "/bs1770gain-" version ".tar.gz"))
        (sha256
         (base32
-         "1p6yz5q7czyf9ard65sp4kawdlkg40cfscr3b24znymmhs3p7rbk"))))
+         "1p6yz5q7czyf9ard65sp4kawdlkg40cfscr3b24znymmhs3p7rbk"))
+       (modules '((guix build utils)))
+       (snippet
+        '(begin
+           ;; XXX
+           (substitute* "bs1770gain/bs1770gain.c"
+             (("\"N.*\"") "\"\""))
+           (substitute* "configure"
+             (("URL=.*$")
+              "https://manpages.debian.org/sid/bs1770gain/bs1770gain.1.en.html\n"))))))
     (build-system gnu-build-system)
     (inputs `(("ffmpeg" ,ffmpeg)
               ("sox" ,sox)))
-    (home-page "http://bs1770gain.sourceforge.net/")
+    (home-page "https://manpages.debian.org/sid/bs1770gain/bs1770gain.1.en.html")
     (synopsis "Tool to adjust loudness of media files")
     (description
      "BS1770GAIN is a loudness scanner compliant with ITU-R BS.1770 and its