angular-cli/packages/angular/cli/commands/add.md

Adds the npm package for a published library to your workspace, and configures the project in the current working directory (or the default project if you are not in a project directory) to use that library, as specified by the library's schematic. For example, adding @angular/pwa configures your project for PWA support:

ng add @angular/pwa

The default project is the value of defaultProject in angular.json.