Nightingale takes after its parents, and has inherited Mozilla's add-ons architecture.
Add-ons are distributed as zipped directories containing an install.rdf among several other files. The best way to get started with making an add-on is to use the Extension Generator. I never use anything else. To distribute your add-on later, simply create a zip of the root directory of your add-on. (If you do it right, unzipping it into a directory will make a mess and not just one folder.)