[TODO] Add kern/GPOS interaction

TODO

diff --git a/TODO b/TODO
index 4df3daf..3bff487 100644
--- a/TODO
+++ b/TODO
@@ -1,3 +1,6 @@
+
+- kern/GPOS interaction
+
 - Use size_t in sanitize?
 - Buffer error handling?
 - Better define HB_INTERNAL