Update configuration.md

Added documentation for `search_tokenizer_separator`.

docs/configuration.md

@@ -28,6 +28,10 @@ View this site's [_config.yml](https://github.com/pmarsceill/just-the-docs/tree/
 # Enable or disable the site search
 # Support true (default) or false
 search_enabled: true
+
+# Enable support for hyphenated search words:
+search_tokenizer_separator: /[\s/]+/
+
 ```
 
 ## Aux links