Update the embedder settings documentation (#3104)

Author: Kerollmops

reference/api/settings.mdx

@@ -2476,7 +2476,7 @@ Use `source` to configure an embedder's source. The following embedders can auto
 
 Additionally, use `rest` to auto-generate embeddings with any embedder offering a REST API.
 
-You may also configure a `userProvided` embedder. In this case, you must manually include vector data in your documents' `_vector` field. You must also manually generate vectors for search queries.
+You may also configure a `userProvided` embedder. In this case, you must manually include vector data in your documents' `_vectors` field. You must also manually generate vectors for search queries.
 
 This field is mandatory.