Update README.md

Author: pierobassa

README.md

@@ -63,7 +63,7 @@ Place your `.env` files in `apps/frontend`:
 
 ### Backend
 
-Store your environment-specific `.env` files in `apps/backend`:
+Store your environment-specific `.env` files in `apps/backend`. `.env.development.local` & `.env.production.local` allow for custom environment variables based on the environment:
 - **OPENAI_API_KEY:** [Get your GPT-4 OpenAI key](https://platform.openai.com/api-keys) (Enable GPT-4 [here](https://help.openai.com/en/articles/7102672-how-can-i-access-gpt-4-gpt-4-turbo-and-gpt-4o))
 - **RECAPTCHA_SECRET_KEY:** [Request your RecaptchaV3 site keys](https://developers.google.com/recaptcha/docs/v3)