fix(doc): mark README entity-RAG code snippet as ignore for doctests

The MetadataBoost example in README uses ? operator and undefined
variables (searcher, query) — it's an API showcase snippet, not a
runnable example. Marking as rust,ignore prevents doctest compilation
failure on Linux CI.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: matte1782

README.md

@@ -119,7 +119,7 @@ python -m http.server 8080
 
 EdgeVec supports **metadata boosting** for entity-enhanced retrieval — improve search relevance by incorporating entity signals (ORG, PERSON, GPE) extracted via NER, without building a knowledge graph.
 
-```rust
+```rust,ignore
 use edgevec::filter::{MetadataBoost, FilteredSearcher, FilterStrategy};
 use edgevec::metadata::MetadataValue;