docs: mention Vitest instead of Karma in README template of schematic library files

Author: guisalmeida

packages/schematics/angular/library/files/README.md.template

@@ -43,7 +43,7 @@ Once the project is built, you can publish your library by following these steps
 
 ## Running unit tests
 
-To execute unit tests with the [Karma](https://karma-runner.github.io) test runner, use the following command:
+To execute unit tests with the [Vitest](https://vitest.dev/) test runner, use the following command:
 
 ```bash
 ng test