Run composer require petrknap/doctrine-entities or merge this JSON code with your project composer.json file manually and run composer install. Instead of dev-master you can use one of released versions.
{
"require": {
"petrknap/doctrine-entities": "dev-master"
}
}
Or manually clone this repository via git clone https://github.com/petrknap/doctrine-entities.git or download this repository as ZIP and extract files into your project.