Instead of downloading an archive you could clone the source code from GitHub. There are a few advantages: first, in this way you will always have the latest bugfixes, even before they are available in a release.
Second, version control makes it easy to upgrade your code, even when you made custom changes in the core of Fork CMS. Only database changes cannot be handled (yet).
If you're not familiar with Git or GitHub yet, here are some good resources to get you started:
In Terminal on Mac OS X or in Command Prompt on Windows, navigate to the root of your project folder and execute this command:
composer install -o
All dependencies are now installed in the vendors folder.
Go through the upgrading guide to find out how you can keep your setup up-to-date with Git.