Add note about adding additional types (#26545)

* Add note about adding additional types

* Update to bold edit also

* Apply suggestions from code review

Co-authored-by: Steven <[email protected]>

Author: ijjk

docs/basic-features/typescript.md

@@ -53,10 +53,12 @@ npm run dev
 
 You're now ready to start converting files from `.js` to `.tsx` and leveraging the benefits of TypeScript!.
 
-> A file named `next-env.d.ts` will be created in the root of your project. This file ensures Next.js types are picked up by the TypeScript compiler. **You cannot remove it**, and it should not be edited as it can change at any time.
+> A file named `next-env.d.ts` will be created in the root of your project. This file ensures Next.js types are picked up by the TypeScript compiler. **You cannot remove it or edit it** as it can change at any time.
 
 > TypeScript `strict` mode is turned off by default. When you feel comfortable with TypeScript, it's recommended to turn it on in your `tsconfig.json`.
 
+> Instead of editing `next-env.d.ts`, you can include additional types by adding a new file e.g. `additional.d.ts` and then referencing it in the [`include`](https://www.typescriptlang.org/tsconfig#include) array in your `tsconfig.json`.
+
 By default, Next.js will do type checking as part of `next build`. We recommend using code editor type checking during development.
 
 If you want to silence the error reports, refer to the documentation for [Ignoring TypeScript errors](/docs/api-reference/next.config.js/ignoring-typescript-errors.md).