add more useful next steps to language tutorial

source/tutorials/nix-language.md

@@ -2037,7 +2037,14 @@ Explanation:
 ### Get things done
 
 - [](declarative-reproducible-envs) – create reproducible shell environments from a Nix file
-- [Garbage Collection](https://nix.dev/manual/nix/2.18/package-management/garbage-collection.html) – remove unused build results from the Nix store
+- [](./packaging-existing-software.md) – make more software available through Nix with one command
+
+
+If you want to take a longer break from learning Nix, you can remove unused build results from the Nix store with:
+
+```console
+$ nix-collect-garbage
+```
 
 ### Learn more