docs(README.md): Update sitemap generation configuration

The commit adds the sitemap plugin and updates the `vite.config.ts` file to include the necessary configuration for generating a sitemap. It also mentions the usage of the `honox` plugin and the `pages` plugin for Cloudflare Pages deployment.

README.md

@@ -505,18 +505,18 @@ export default defineConfig(({ mode }) => {
           output: {
             entryFileNames: 'static/client.js',
             chunkFileNames: 'static/assets/[name]-[hash].js',
-            assetFileNames: 'static/assets/[name].[ext]'
-          }
+            assetFileNames: 'static/assets/[name].[ext]',
+          },
         },
-        emptyOutDir: false
-      }
+        emptyOutDir: false,
+      },
     }
   } else {
     return {
       ssr: {
-        external: ['react', 'react-dom']
+        external: ['react', 'react-dom'],
       },
-      plugins: [honox(), pages()]
+      plugins: [honox(), pages()],
     }
   }
 })
@@ -815,6 +815,72 @@ export default defineConfig({
 })
 ```
 
+### Generate Sitemap
+
+To generate a sitemap, use the `sitemap` plugin provided by HonoX.
+
+Update your `vite.config.ts` as follows:
+
+```ts
+import honox from 'honox/vite'
+import adapter from '@hono/vite-dev-server/cloudflare'
+import { defineConfig } from 'vite'
+import sitemap from 'honox/vite/sitemap'
+
+export default defineConfig({
+  plugins: [
+    honox({
+      devServer: {
+        adapter,
+      },
+    }),
+    sitemap({
+      hostname: 'https://example.com',
+      exclude: ['/404', 'error'],
+      priority: { '/': '1.0', '/about': '0.8', '/posts/*': '0.6' },
+      frequency: { '/': 'daily', '/about': 'monthly', '/posts/*': 'weekly' },
+    }),
+  ],
+})
+```
+
+For deployment to Cloudflare Pages, you can use the following configuration:
+
+Register the IS_PROD = true environment variable in the Cloudflare Pages settings:
+
+1. Navigate to the Cloudflare Workers & Pages Dashboard.
+1. Go to [Settings] -> [Environment Variables] -> [Production]
+1. Add `IS_PROD` with the value `true`.
+
+Update your `vite.config.ts`:
+
+```ts
+import pages from '@hono/vite-cloudflare-pages'
+import honox from 'honox/vite'
+import adapter from '@hono/vite-dev-server/cloudflare'
+import { defineConfig } from 'vite'
+import sitemap from 'honox/vite/sitemap'
+
+export default defineConfig({
+  plugins: [
+    honox({
+      devServer: {
+        adapter,
+      },
+    }),
+    pages(),
+    sitemap({
+      hostname: process.env.IS_PROD
+        ? 'https://your-project-name.pages.dev/'
+        : process.env.CF_PAGES_URL,
+    }),
+  ],
+})
+```
+
+Note: `CF_PAGES_URL` is an environment variable that Cloudflare Pages automatically sets.
+For more information, see [Environment Variables](https://developers.cloudflare.com/pages/configuration/build-configuration/#environment-variables).
+
 ## Deployment
 
 Since a HonoX instance is essentially a Hono instance, it can be deployed on any platform that Hono supports.