feat: Tracking input tokens on embeddings store ingestor (langchain4j…

…#1907)

docs/docs/tutorials/7-rag.md

@@ -528,9 +528,13 @@ EmbeddingStoreIngestor ingestor = EmbeddingStoreIngestor.builder()
 
 ingestor.ingest(document1);
 ingestor.ingest(document2, document3);
-ingestor.ingest(List.of(document4, document5, document6));
+IngestionResult ingestionResult = ingestor.ingest(List.of(document4, document5, document6));
 ```
 
+All `ingest()` methods in `EmbeddingStoreIngestor` return an `IngestionResult`.
+The `IngestionResult` contains useful information, including `TokenUsage`,
+which shows how many tokens were used for embedding.
+
 Optionally, the `EmbeddingStoreIngestor` can transform `Document`s using a specified `DocumentTransformer`.
 This can be useful if you want to clean, enrich, or format `Document`s before embedding them.