Add Missing Type Imports to Readme

Basic Usage Code Snippets are missing imports for SearchResult and ModelSpanExtractor.
Added them for completeness.

README.md

@@ -54,6 +54,9 @@ The model requires the following key dependencies:
 ### Basic Usage
 
 ```python
+from verbatim_rag.vector_stores import SearchResult
+from verbatim_core.extractors import ModelSpanExtractor
+
 extractor = ModelSpanExtractor(
     model_path="KRLabsOrg/verbatim-rag-modern-bert-v1",
 )