[gtkmm] Mark the branch in the ChangeLog

[Murray Cumming <murrayc src gnome org>]

commit 9a8ce8ee34915c7fb471bb40eead1ff984317043
Author: Murray Cumming <murrayc murrayc com>
Date:   Mon May 17 21:22:28 2010 +0200

    Mark the branch in the ChangeLog

 ChangeLog |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 3c0f255..ae8942c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -174,6 +174,9 @@
 	* gtk/src/widget.hg: Remove use of the no_default_handler option with 
 	_WRAP_SIGNAL(), breaking ABI by adding virtual methods.
 
+This is the master branch, for the planned API/ABI-breaking gtkmm 3.
+See also the gtkmm-2-20 and gtkmm-2-22 branches.
+
 2.20.3:
 
 2010-05-04  Murray Cumming  <murrayc murrayc com>