doc: Add duplicate copyright notice again.

* doc/guix.texi: Add second copyright notice again inside @ifinfo, needed
  since the first one does not appear in the info output.
  Partially undoes commit da7cabd4.

doc/guix.texi

@@ -33,6 +33,7 @@ Edition @value{EDITION} @*
 
 Copyright @copyright{} @value{YEARS} Ludovic Court@`es, Andreas Enge, Nikita Karetnikov
 
+@ifinfo
 @quotation
 Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.3 or
@@ -41,6 +42,8 @@ Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.  A
 copy of the license is included in the section entitled ``GNU Free
 Documentation License''.
 @end quotation
+@end ifinfo
+
 @end titlepage
 
 @copying
@@ -65,6 +68,18 @@ Documentation License.''
 This document describes GNU Guix version @value{VERSION}, a functional
 package management tool written for the GNU system.
 
+
+@quotation
+Copyright @copyright{} @value{YEARS} Ludovic Courtès, Andreas Enge, Nikita Karetnikov
+
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License, Version 1.3 or
+any later version published by the Free Software Foundation; with no
+Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.  A
+copy of the license is included in the section entitled ``GNU Free
+Documentation License.''
+@end quotation
+
 @menu
 * Introduction::                What is Guix about?
 * Installation::                Installing Guix.