docs: add default module definition systems (#878)

Author: Timeless0911

website/docs/en/config/lib/format.mdx

@@ -13,3 +13,11 @@ See [Output Format](/guide/basic/output-format) and [Module Federation](/guide/a
 The `umd` format only works when [bundle](/config/lib/bundle) is set to `true`.
 
 :::
+
+## Module definition systems
+
+In different output formats, Rslib uses the following default module definition systems:
+
+- `esm`：[modern-module](https://rspack.dev/config/output#type-modern-module)
+- `cjs`：[commonjs-static](https://rspack.dev/config/output#type-commonjs-static)
+- `umd`：[umd](https://rspack.dev/config/output#type-umd)

website/docs/zh/config/lib/format.mdx

@@ -11,3 +11,11 @@
 ::: note
 `umd` 格式仅在 [bundle](/config/lib/bundle) 设置为 `true` 时有效。
 :::
+
+## 模块定义系统
+
+在不同的产物格式下，Rslib 默认使用的模块定义系统如下：
+
+- `esm`：[modern-module](https://rspack.dev/zh/config/output#type-modern-module)
+- `cjs`：[commonjs-static](https://rspack.dev/zh/config/output#type-commonjs-static)
+- `umd`：[umd](https://rspack.dev/zh/config/output#type-umd)