Add link to customization.mdx

Author: shivansh

fern/docs/pages/custom-objects.mdx

@@ -167,6 +167,8 @@ curl --location 'https://api.devrev.ai/custom-objects.delete' \
 3. **Custom Fields**: User-defined fields that store specific data for your custom object.
 4. **Unique Key**: A unique identifier for each custom object, useful for maintaining idempotency.
 
+For more details, please refer to the [Customization](./customization.mdx) documentation.
+
 ## Custom Object Lifecycle
 
 1. **Creation**: Define the leaf type, subtype (optional), and custom fields for your object.