Update release notes a bit

README.in

@@ -73,6 +73,18 @@ Patches should be in unified diff form. (The -up option to GNU diff)
 Even better are git-formatted patches. (Use git format-patch)
 
 
+Release notes for 3.18
+======================
+
+* The GtkListBox model support that was introduced in 3.16 has been
+  changed to no longer call gtk_widget_show_all on rows created by
+  the create_widget_func. You need to manage the visibility of child
+  widgets yourself in your create_widget_func.
+
+* The alpha component of foreground colors that are applied to
+  GtkCellRendererText is no longer ignored. If you don't want your
+  text to be translucent, use opaque colors.
+
 Release notes for 3.16
 ======================
 
@@ -99,7 +111,7 @@ Release notes for 3.16
   has non-scrolling parts similar to treeview headers, there is no need
   to implement this vfunc.
 
-* The GtkSearchEntry widget has gained a number of new signal that
+* The GtkSearchEntry widget has gained a number of new signals that
   are emitted when certain key sequences are seen. In particular, it
   now handles the Escape key and emits ::stop-search. Applications that
   expect to handle Escape themselves will need to be updated.