add composer.json

With this change, this is now possible:

    {
        "name": "wpsite/tom-j-nowell",
        "description": "",
        "homepage": "http://www.tomjn.com",
        "version": "3.6.1",
        "repositories": [
            {
                "type": "git",
                "url": "https://github.com/inpsyde/Inpsyde-oEmbed-Gist.git"
            },
        ],
        "require": {
            "johnpbloch/wordpress": ">=3.6.1",
            "php": ">=5.3.2",
            "inpsyde/oembed-gist": ">=1.0.3"
        }
    }

This will install Wordpress 3.6.1 with the oembed gist plugin installed