Briefing
A SHA-256 digest is a fingerprint for file contents. checksum.txt records the digest of the *genuine* file. Compute the digest of both candidates with sha256sum and compare.
Objective Find which file matches the digest in checksum.txt, then read it.
Stuck?
Take it one step at a time. Ask for a hint here, or type help in the terminal to
see the commands this challenge is about. Typing hint works there too.
That is every hint. If you are still stuck, run help in the terminal.