Simply post a thread in
the Key Distribution forum and we'll reply with a key. Only you and the dev team will be able to see threads in that section.
Feel free to request multiple keys if you have friends that don't have a forum account.
Once you get your key: In Steam, go to
Games -> Activate a Product on Steam and enter your key. This will start the installation process.
If you'd like a Dedicated Server key as well, let us know in your thread.