docs(metro-plugin-cyclic-dependencies-detector): fix Expo example

Author: tido64

.changeset/shiny-snakes-behave.md

@@ -0,0 +1,2 @@
+---
+---

packages/metro-plugin-cyclic-dependencies-detector/README.md

@@ -36,11 +36,15 @@ directly in your `metro.config.js`. This is useful if you are using Expo which
 uses its own custom serializer:
 
 ```js
+const {
+  CyclicDependencies,
+} = require("@rnx-kit/metro-plugin-cyclic-dependencies-detector");
 const { getDefaultConfig } = require("expo/metro-config");
 
 /** @type {import('expo/metro-config').MetroConfig} */
 const config = getDefaultConfig(__dirname);
 
+const expoSerializer = config.serializer.customSerializer;
 config.serializer.customSerializer = async (
   entryPoint,
   preModules,
@@ -50,12 +54,7 @@ config.serializer.customSerializer = async (
   CyclicDependencies({
     // Options
   })(entryPoint, preModules, graph, options);
-  return await config.serializer.customSerializer(
-    entryPoint,
-    preModules,
-    graph,
-    options
-  );
+  return await expoSerializer(entryPoint, preModules, graph, options);
 };
 
 module.exports = config;
@@ -68,3 +67,10 @@ module.exports = config;
 | includeNodeModules | boolean | `false` | Whether to scan `node_modules`.               |
 | linesOfContext     | number  | 1       | Number of extra modules to print for context. |
 | throwOnError       | boolean | `true`  | Whether to throw when cycles are detected.    |
+
+## Limitations
+
+- This plugin can only detect cycles that are present in the module graph
+  generated by Metro. If your project uses file based routing (e.g. Expo
+  Router), Metro may not include every file in its module graph. Consequently,
+  this plugin cannot detect cycles outside of the graph.