Add Dockerfile

After building promdash image by doing:

    $ docker build -t promdash .

You can create the database by:

    $ docker run -t -i -link mysqld:db \
        -e PROMDASH_MYSQL_DATABASE=<database> \
        -e PROMDASH_MYSQL_USERNAME=<user> \
        -e PROMDASH_MYSQL_PASSWORD=<pass> \
        -p promdash rake db:setup

(You can also set DATABASE_URL if you can use docker links)

Now you can run promdash like this:

    $ docker run -t -i -link mysqld:db \
        -e PROMDASH_MYSQL_DATABASE=<database> \
        -e PROMDASH_MYSQL_USERNAME=<user> \
        -e PROMDASH_MYSQL_PASSWORD=<pass> \
        -p 3000 promdash