[gtksourceview] Add comment in configure.ac about last commit

[Sébastien Wilmet <swilmet src gnome org>]

commit affae0222e39f6f31c1adb10c3d02bca9e9c73cf
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Thu Oct 1 20:16:35 2015 +0200

    Add comment in configure.ac about last commit
    
    To not forget it, if someone in the future wants to remove the ChangeLog
    file.

 configure.ac |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 138c441..50461dc 100644
--- a/configure.ac
+++ b/configure.ac
@@ -46,6 +46,7 @@ AC_CONFIG_SRCDIR([gtksourceview/gtksourcebuffer.h])
 AC_CONFIG_HEADER([config.h])
 AC_CONFIG_MACRO_DIR([m4])
 
+# gnu strictness to generate the INSTALL file
 AM_INIT_AUTOMAKE([1.13 tar-ustar dist-xz no-dist-gzip -Wno-portability gnu])
 AM_MAINTAINER_MODE([enable])