docs: add note about import.meta.env with TS (#2773)

docs/guide/env-and-mode.md

@@ -51,6 +51,19 @@ Only `VITE_SOME_KEY` will be exposed as `import.meta.env.VITE_SOME_KEY` to your
 - Since any variables exposed to your Vite source code will end up in your client bundle, `VITE_*` variables should _not_ contain any sensitive information.
   :::
 
+### IntelliSense
+
+By default, Vite provides type definition for `import.meta.env`. While you can define more custom env variables in `.env.[mode]` files, you may want to get TypeScript IntelliSense for user-defined env variables which prefixed with `VITE_`.
+
+To achieve, you can create an `env.d.ts` in `src` directory, then augment `ImportMetaEnv` like this:
+
+```typescript
+interface ImportMetaEnv {
+  VITE_APP_TITLE: string
+  // more env variables...
+}
+```
+
 ## Modes
 
 By default, the dev server (`serve` command) runs in `development` mode, and the `build` command runs in `production` mode.