chore: minor adjustment of docs

docs/source/usage.rst

@@ -100,7 +100,7 @@ the instance method persists and exposes the reference cache and provides helper
 .. warning::
     The instance API with reference cache can lead to schema and type name collisions if not managed carefully.
     It's recommended that each schema defines its own unique namespace using the `$id` property in JSON Schema,
-    and that access it's ref_cache by passing it explicitly when needed.
+    and then access it's ref_cache by passing it explicitly when needed.
     
 For details and examples about the reference cache and the different cache modes (instance cache, per-call cache, ephemeral cache), see: