If you're new here, read contributing sector.
It's good to make a separate directory for single level in the levels directory, but it's also OK to make a directory for series of levels or even personal author catalog.
This folder should contain main level file, can contain assets and other files that might be used.
Every level and all its files have to be indexed.
After you've did it all (in your fork of this repo), you're free to make a pull request and publish your level here.