With composer:
$ composer config repositories.m2-sysint-backend vcs https://github.com/sysintnet/m2-sysint-backend.git
$ composer require sysintnet/m2-sysint-backend:dev-master
Manually:
Copy the zip into ../app/code/Sysint/Backend
directory
$ php bin/magento module:enable Sysint_Backend --clear-static-content
$ php bin/magento setup:upgrade