Update changes.md for TIP 737

Author: apnadkarni

changes.md

@@ -22,6 +22,7 @@ writing Tcl scripts.
 - [Tcl\_AttemptCreateHashEntry - version of Tcl\_CreateHashEntry that returns NULL instead of panic'ing on memory allocation errors](https://core.tcl-lang.org/tips/doc/trunk/tip/717.md)
 - [Tcl\_ListObjRange, Tcl\_ListObjRepeat, Tcl\_TclListObjReverse - C API for new list operations](https://core.tcl-lang.org/tips/doc/trunk/tip/649.md)
 - [Tcl\_UtfToNormalized, Tcl\_UtfToNormalizedDString - C API for Unicode normalization](https://core.tcl-lang.org/tips/doc/trunk/tip/726.md)
+- [Tcl\_UtfToExternalEx and Tcl\_ExternalToUtfEx - C encoding API supporting output buffers larger than INT_MAX](https://core.tcl-lang.org/tips/doc/trunk/tip/737.md)
 
 # Performance