Update release_notes.txt
Update release_notes.txt

To include pending changes to 7.2.7 release
lcorbasson/libphonenumber,google/libphonenumber,google/libphonenumber,keghani/libphonenumber,google/libphonenumber,keghani/libphonenumber,lcorbasson/libphonenumber,google/libphonenumber,google/libphonenumber,lcorbasson/libphonenumber,lcorbasson/libphonenumber,google/libphonenumber,keghani/libphonenumber,keghani/libphonenumber,keghani/libphonenumber,lcorbasson/libphonenumber