GitHub tables don’t support checkboxes, but you can fake it with Unicode symbols. I’ve used ✓ and ✗ in my docs for years - just copy/paste them directly into table cells. ✓ for done, ✗ for not done, or leave blank. You can also use HTML entities like ✓ and ✗ if you prefer. Both render fine on GitHub and give you the visual status you want.