docs: update ts-config override examples

docs/advanced/making plugins.md

@@ -645,14 +645,21 @@ plugins:
     enabled: true
 ```
 
-Or via TS override in `quartz.ts`:
+For options that require JavaScript callback functions (not expressible in YAML), use the TS override in `quartz.ts`:
 
 ```ts title="quartz.ts (override)"
 import * as ExternalPlugin from "./.quartz/plugins"
-// ...
-transformers: [ExternalPlugin.MyPlugin()]
+
+ExternalPlugin.MyPlugin({
+  // callback functions or other non-serializable options
+  customFn: (data) => {
+    // ...
+  },
+})
 ```
 
+Options set via `quartz.ts` are merged with YAML options at instantiation time, with `quartz.ts` overrides taking precedence.
+
 ### Development Workflow
 
 During plugin development, you'll frequently install and uninstall your plugin to test changes. The following commands help manage this cycle: