use rust,ignore code fences in readme.md (fix #34)

so that we no longer need to add `--skip` on `cargo test`

CONTRIBUTING.md

@@ -21,11 +21,9 @@ Please ensure that all tests and linter checks passed on your branch before crea
 To run tests:
 
 ```sh
-cargo test --features=search -- --skip src/lib.rs
+cargo test --features=search
 ```
 
-`--skip` is necessary since `cargo test` tries to run code blocks in [README file](./README.md).
-
 To run linters:
 
 ```sh