In order to install module, you can do it two ways:

1. Install By Composer
   1. Take clone
   2. run composer require sb/module-default-qty
   3. Run necessary magento commands like setup:upgrade, di:compile, static-content:deploy
2. Install From App/Code
   1. Clone and Just extract zip and paste Sb/DefaultQty directory inside app/code
   2. Run necessary magento commands like setup:upgrade, di:compile, static-content:deploy