doc: document ESM configuration

Author: thescientist13

docs-next/src/content/docs/running/configuring.mdx

@@ -9,7 +9,8 @@ title: Configuring Mocha (Node.js)
 Mocha supports configuration files, typical of modern command-line tools, in several formats:
 
 - **JavaScript**: Create a `.mocharc.js` (or `.mocharc.cjs` when using [`"type"="module"`](/explainers/nodejs-native-esm-support) in your `package.json`)
-  in your project's root directory, and export an object (`module.exports = {/* ... */}`) containing your configuration.
+  in your project's root directory, and export an object (`module.exports = {/* ... */}`) containing your configuration.  For native ESM and using `type="module"`
+  or using `.mjs`, use a default export (`default export  {/* ... */}`).
 - **YAML**: Create a `.mocharc.yaml` (or `.mocharc.yml`) in your project's root directory.
 - **JSON**: Create a `.mocharc.json` (or `.mocharc.jsonc`) in your project's root directory.
   Comments--while not valid JSON--are allowed in this file, and will be ignored by Mocha.

docs/index.md

@@ -2254,7 +2254,9 @@ The HTML reporter is the default reporter when running Mocha in the browser. It
 
 Mocha supports configuration files, typical of modern command-line tools, in several formats:
 
-- **JavaScript**: Create a `.mocharc.js` (or `.mocharc.cjs` when using [`"type"="module"`](#nodejs-native-esm-support) in your `package.json`)
+- **JavaScript**: Create a `.mocharc.js` (or `.mocharc.cjs` when using [`"type"="module"`](/explainers/nodejs-native-esm-support) in your `package.json`)
+  in your project's root directory, and export an object (`module.exports = {/* ... */}`) containing your configuration.  For native ESM and using `type="module"`
+  or using `.mjs`, use a default export (`default export  {/* ... */}`).
   in your project's root directory, and export an object (`module.exports = {/* ... */}`) containing your configuration.
 - **YAML**: Create a `.mocharc.yaml` (or `.mocharc.yml`) in your project's root directory.
 - **JSON**: Create a `.mocharc.json` (or `.mocharc.jsonc`) in your project's root directory. Comments — while not valid JSON — are allowed in this file, and will be ignored by Mocha.