add a line about logging in

Author: SBrandeis

docs/api-inference/rate-limits.md

@@ -4,6 +4,9 @@ The Inference API has rate limits based on the number of requests. These rate li
 
 Serverless API is not meant to be used for heavy production applications. If you need higher rate limits, consider [Inference Endpoints](https://huggingface.co/docs/inference-endpoints) to have dedicated resources.
 
+Only registered users can use the Inference API.
+
+
 | User Tier           | Rate Limit                |
 |---------------------|---------------------------|
 | Signed-up Users     | 1.000 requests per day     |