Battlechain tutorial
npx -y skills add Cyfrin/solskill --skill battlechain-tutorialAssembled from the repository path, not quoted from the project. Check it against their README if it does not work.
Keep looking
Skills are one crate of 628,853. Ordering is by how many stacks a row turns up in, so the top of any crate is what has actually been picked rather than what has the most stars.