Blobs usually represent the content of a file. But on their own, they don't have any metadata, not even a name!

Git has a very powerful concept to store metadata related to blobs: the index! It's a list that relates blobs to filenames and access permissions.

The most convenient option to add an entry to the index is via an existing file:

    echo "my content" > file
    git update-index --add file

Add three entries to the index! For a bonus challenge: can you add a file that is inside of a directory, like "directory/file"?