Fix syntax in Swift config example (SDKs) (#592)

Author: devalog

fern/products/sdks/overview/swift/configuration.mdx

@@ -5,15 +5,16 @@ description: Configuration options for the Fern Swift SDK.
 
 You can customize the behavior of the Swift SDK generator in `generators.yml`:
 
-```yaml {7-8} title="generators.yml"
+```yaml {7-9} title="generators.yml"
 default-group: local
 groups:
   local:
     generators:
       - name: fernapi/fern-swift-sdk
         version: <Markdown src="/snippets/version-number-swift.mdx"/>
-        clientClassName: YourClientName
-        environmentEnumName: YourCustomEnvironment
+        config:
+          clientClassName: YourClientName
+          environmentEnumName: YourCustomEnvironment
 ```
 
 ## SDK Configuration Options