feat: describe `addServerHandler`

docs/3.api/4.advanced/2.kit.md

@@ -2029,11 +2029,122 @@ export default defineNuxtModule({
 
 [source code](https://github.com/nuxt/nuxt/blob/main/packages/kit/src/nitro.ts)
 
-### `addServerHandler (handler)`
+### `addServerHandler`
+
+Adds a nitro server handler.
+
+#### Type
+
+```ts
+function addServerHandler (handler: NitroEventHandler): void
+
+export interface NitroEventHandler {
+  handler: string;
+  route?: string;
+  middleware?: boolean;
+  lazy?: boolean;
+  method?: string;
+}
+```
+
+#### Parameters
+
+##### `handler`
+
+**Type**: `NitroEventHandler`
+
+**Required**: `true`
+
+A handler object with the following properties:
+
+- `handler` (required)
+
+  **Type**: `string`
+
+  Path to event handler.
+
+- `route` (optional)
+
+  **Type**: `string`
+
+  Path prefix or route. If an empty string used, will be used as a middleware.
+
+- `middleware` (optional)
+
+  **Type**: `boolean`
+
+  Specifies this is a middleware handler. Middleware are called on every route and should normally return nothing to pass to the next handlers.
+
+- `lazy` (optional)
+
+  **Type**: `boolean`
+
+  Use lazy loading to import handler.
+
+- `method` (optional)
+
+  **Type**: `string`
+
+  Router method matcher.
 
 ### `addDevServerHandler (handler)`
 
-### `useNitro()` (only usable after `ready` hook)
+### `useNitro`
+
+Returns the Nitro instance.
+
+::alert{type=warning}
+You can call `useNitro()` only after `ready` hook.
+::
+
+::alert{type=info}
+Changes to the Nitro instance configuration are not applied.
+::
+
+#### Type
+
+```ts
+function useNitro (): Nitro
+
+export interface Nitro {
+  options: NitroOptions;
+  scannedHandlers: NitroEventHandler[];
+  vfs: Record<string, string>;
+  hooks: Hookable<NitroHooks>;
+  unimport?: Unimport;
+  logger: ConsolaInstance;
+  storage: Storage;
+  close: () => Promise<void>;
+  updateConfig: (config: NitroDynamicConfig) => void | Promise<void>;
+}
+```
+
+#### Examples
+
+```ts
+// https://github.com/nuxt/nuxt/blob/4e05650cde31ca73be4d14b1f0d23c7854008749/packages/nuxt/src/core/nuxt.ts#L404
+import { defineNuxtModule, useNitro, addPlugin, createResolver } from '@nuxt/kit'
+
+export default defineNuxtModule({
+  setup(options, nuxt) {
+    const { resolve } = createResolver(import.meta.url)
+
+    nuxt.hook('ready', () => {
+      const nitro = useNitro()
+      if (nitro.options.static && nuxt.options.experimental.payloadExtraction === undefined) {
+        console.warn('Using experimental payload extraction for full-static output. You can opt-out by setting `experimental.payloadExtraction` to `false`.')
+        nuxt.options.experimental.payloadExtraction = true
+      }
+      nitro.options.replace['process.env.NUXT_PAYLOAD_EXTRACTION'] = String(!!nuxt.options.experimental.payloadExtraction)
+      nitro.options._config.replace!['process.env.NUXT_PAYLOAD_EXTRACTION'] = String(!!nuxt.options.experimental.payloadExtraction)
+
+      if (!nuxt.options.dev && nuxt.options.experimental.payloadExtraction) {
+        addPlugin(resolve(nuxt.options.appDir, 'plugins/payload.client'))
+      }
+    })
+  }
+})
+```
 
 ### `addServerPlugin`