[meld] ui.notebook: Add some class docstring

[Kai Willadsen <kaiw src gnome org>]

commit 53bf59a87176b9cda85e07cbb72c60267669703e
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Thu Dec 10 05:42:28 2015 +1000

    ui.notebook: Add some class docstring

 meld/ui/notebook.py |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/meld/ui/notebook.py b/meld/ui/notebook.py
index 1a50f89..ebd800c 100644
--- a/meld/ui/notebook.py
+++ b/meld/ui/notebook.py
@@ -20,6 +20,12 @@ from gi.repository import Gtk
 
 
 class MeldNotebook(Gtk.Notebook):
+    """Notebook subclass with tab switch and reordering behaviour
+
+    MeldNotebook implements some fairly generic tab switching shortcuts
+    and a popup menu for simple tab controls, as well as some
+    Meld-specific tab label handling.
+    """
 
     __gtype_name__ = "MeldNotebook"