scripts: indicate how to see scripts-descriptions (#8823)

* scripts: indicate how to see scripts-descriptions

* Update scripts.md

Co-authored-by: Jordi Boggiano <j.boggiano@seld.be>

doc/articles/scripts.md

@@ -375,4 +375,7 @@ You can set custom script descriptions with the following in your `composer.json
 }
 ```
 
+The descriptions are used in `composer list` or `composer run -l` commands to
+describe what the scripts do when the command is run.
+
 > **Note:** You can only set custom descriptions of custom commands.