Add missing contributors to the CONTRIBUTORS.md

[damithc]

These tutors helped to write the initial version of the Schedule page, but they are missing from the contributor list.
week 3: Junwei
week 4: Chun Kit
week 5: Lynnette
week 6: Ryan
week 7: Fazli
week 8: Karan
week 9: Asawari
week 10: Sebastian
week 11: Ian
week 12: Sam
week 13: Junchao

Their full names can be found in this page

Their GitHub IDs can be found by digging through past PRs.