describe usage for text search in document

CONTRIBUTING.md

@@ -21,7 +21,7 @@ Please ensure that all tests and linter checks passed on your branch before crea
 To run tests:
 
 ```sh
-cargo test -- --skip src/lib.rs
+cargo test --features=search -- --skip src/lib.rs
 ```
 
 `--skip` is necessary since `cargo test` tries to run code blocks in [README file](./README.md).