[gtkmm] Marked the branch in the ChangeLog

[Murray Cumming <murrayc src gnome org>]

commit b5949a6b197f7f29e377830c1bdafbaf2b26b463
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Nov 27 14:36:16 2009 +0100

    Marked the branch in the ChangeLog

 ChangeLog |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 5f29d26..0335d96 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -12,6 +12,8 @@
 	* configure.ac: Require a newer version of GTK+.
 	Bug #598715.
 
+This is the master branch. See also the gtkmm-2-18 branch.
+
 2009-10-30  Murray Cumming  <murrayc murrayc com>
 
 	VPaned documentation now says that it's vertical.