docs: note about unknown variables

Close #27

README.md

@@ -263,9 +263,23 @@ interface ImportMetaEnv extends ImportMetaEnvAugmented {
   // Now import.meta.env is totally type-safe and based on your `env.ts` schema definition
   // You can also add custom variables that are not defined in your schema
 }
+```
+
+## Forbid unknown variables
+
+Since we rely on module augmentation to type `import.meta.env`, using unknown variables won’t trigger errors because the `ImportMetaEnv` interface from Vite includes a `[key: string]: string` signature.
+
+To enforce stricter typing and prevent the use of unknown variables, you can set up the following:
 
+```ts
+// lib/env.ts or wherever you want
+import { ImportMetaEnvAugmented } from '@julr/vite-plugin-validate-env';
+
+export const env: ImportMetaEnvAugmented = import.meta.env;
 ```
 
+By using `env` instead of `import.meta.env` in your code, TypeScript will now throw an error if you try to access an unknown variable.
+
 ## Sponsors
 
 If you like this project, [please consider supporting it by sponsoring it](https://github.com/sponsors/Julien-R44/). It will help a lot to maintain and improve it. Thanks a lot !