docs(node): add info about constraints option (#14576)

docs/usage/node.md

@@ -37,3 +37,5 @@ For example, if you want to use at least npm `8.1.0` and also allow newer versio
   }
 }
 ```
+
+Alternatively, the npm version can also be configured via the [`constraints` option](https://docs.renovatebot.com/configuration-options/#constraints).