CNC group work
images added and week04 and week05.md changes. Make sure this does not conflict with the students' pages.
We're still debating whether it's easier to push to our fork and submit MR, or push to the page directly. Let me know if you have a preference. Pushing to a fork makes it easier to revert accidental pushes with large files but may add headaches when there are two MRs open at a time or two MRs conflict.