docs(plugins): add a note for resourceRegExp

Author: chenxsan

src/content/plugins/normal-module-replacement-plugin.mdx

@@ -4,6 +4,7 @@ group: webpack
 contributors:
   - gonzoyumo
   - byzyk
+  - chenxsan
 ---
 
 The `NormalModuleReplacementPlugin` allows you to replace resources that match `resourceRegExp` with `newResource`. If `newResource` is relative, it is resolved relative to the previous resource. If `newResource` is a function, it is expected to overwrite the request attribute of the supplied resource.
@@ -14,6 +15,8 @@ This can be useful for allowing different behaviour between builds.
 new webpack.NormalModuleReplacementPlugin(resourceRegExp, newResource);
 ```
 
+Note that the `resourceRegExp` is tested against the request you write in your code, not the resolved resource. For instance, `'./sum'` will be used to test instead of `./sum.js` when you have code `import sum from './sum'`.
+
 ## Basic Example
 
 Replace a specific module when building for a [development environment](/guides/production).