doc(test): Add the test command line in readme and how to use it (#140)

Co-authored-by: DanCodes <dan@dancodes.online>
Co-authored-by: Vladimir <vladimir@bourseauxlivres.fr>

README.md

@@ -96,6 +96,20 @@ Don't forget to give the project a star! Thanks again!
 4. Push to the Branch (`git push origin feature/AmazingFeature`)
 5. Open a Pull Request
 
+## Testing
+
+The project is tested with `vitest` and requires you to have a library on your BunnyCDN account to send commands to the Bunny API. 
+
+> Warning: all videos will be deleted during testing.
+
+### Keys
+
+```sh
+BUNNY_VIDEO_LIBRARY=xxx BUNNY_API_KEY=xxx npm test
+```
+
+Also, `IGNORE_PRUNE=1` can be used to keep the testing video at the end of the tests for further manual checking.
+
 <!-- LICENSE -->
 
 ## License