Sample composer.json file

composer.json

{
    "name": "vendor/modulename",
    "type": "magento-module",
    "license":"OSL-3.0",
    "description":"Helps you doing cool stuff",
    "authors":[
        {
            "name":"Firstname Lastname",
            "email":"firstname.lastname@awesomecompany.com"
        }
    ],
    "require": {
        "magento-hackathon/magento-composer-installer": "*"
    }
}