Fix tiny typo, screen -> screens (#282)

Currently links to


https://github.com/TheBevyFlock/bevy_quickstart/blob/main/src/screen/credits.rs

but should be


https://github.com/TheBevyFlock/bevy_quickstart/blob/main/src/screens/credits.rs

README.md

@@ -121,4 +121,4 @@ The CC0 license explicitly does not waive patent rights, but we confirm that we
 
 ## Credits
 
-The [assets](./assets) in this repository are all 3rd-party. See the [credits screen](./src/screen/credits.rs) for more information.
+The [assets](./assets) in this repository are all 3rd-party. See the [credits screen](./src/screens/credits.rs) for more information.