docs: add more keywords for reducer/reviver docs

#21832 (comment)

docs/3.api/2.composables/use-nuxt-app.md

@@ -128,9 +128,9 @@ Nuxt exposes the following properties through `ssrContext`:
 
   It is also possible to use more advanced types, such as `ref`, `reactive`, `shallowRef`, `shallowReactive` and `NuxtError`.
 
-  Since [Nuxt v3.4](https://nuxt.com/blog/v3-4#payload-enhancements), it is possible to define your own serializer/deserializer for types that are not supported by Nuxt.
+  Since [Nuxt v3.4](https://nuxt.com/blog/v3-4#payload-enhancements), it is possible to define your own reducer/reviver for types that are not supported by Nuxt.
 
-  In the example below, we define a serializer for the [Luxon](https://moment.github.io/luxon/#/) DateTime class.
+  In the example below, we define a reducer (or a serializer) and a reviver (or deserializer) for the [Luxon](https://moment.github.io/luxon/#/) DateTime class, using a payload plugin.
 
   ```ts [plugins/date-time-payload.ts]
   /**