fixed minor typo
edited calcgrade.sh so unverified signatures don't show as "bad signature" and instead say "signed but untrusted". Students aren't likely to have a web of trust that includes the instructors.
added a function that will check if a key already exists in repository
Adds signing key to repository if it does not already exist
addgrader.sh will now append new keys instead of overwriting
Update README.md
Update README.md
Merge pull request #318 from Liniarc/new

Students can now see signed commits. Fixed typo in config.sh
Update README.md
fixing conflict