Update docs/index.md

Co-authored-by: Samuel Colvin <[email protected]>

docs/index.md

@@ -85,7 +85,7 @@ print(Settings().model_dump())
 1. The environment variable name is overridden using `validation_alias`. In this case, the environment variable
    `my_auth_key` will be read instead of `auth_key`.
 
-    Check the [`Field` documentation](fields.md) for more information.
+    Check the [`Field` documentation](../usage/fields.md) for more information.
 
 2. The environment variable name is overridden using `alias`. In this case, the environment variable
    `my_api_key` will be used for both validation and serialization instead of `api_key`.