docs: add introduction and features doc

Author: Timeless0911

website/docs/en/guide/start/index.mdx

@@ -1,12 +1,30 @@
 # Introduction
 
+Rslib is a library build tool that leverages the excellent configurations and plugins of Rsbuild, empowering library developers to take advantage of the extensive knowledge and ecosystem of webpack and Rspack.
+
+Rslib provides a comprehensive set of [build features](/guide/start/features) for library development, including:
+
+- **Compilation of diverse languages**: TypeScript, JSX, Sass, Less, CSS Modules, Wasm, and more.
+- **Flexible build modes**: Bundle and bundleless options to suit your needs.
+- **Multiple output formats**: ESM, CJS, and UMD for maximum compatibility.
+- **Declaration file generation**: Including isolated declarations.
+- **Advanced features**: Module Federation, asset compression, PostCSS, Lightning CSS, and more.
+
 ## 🔥 Features
 
+Rslib has the following features:
+
+- **Easy to Configure**: Rslib aims to simplify library development by offering ready-to-use build capabilities, enabling developers to kickstart their library projects with minimal configuration.
+
+- **Performance Oriented**: Rslib integrates high-performance Rust-based tools from the community, including Rspack, SWC and Lightning CSS, to deliver first-class build speed and development experience.
+
+- **Plugin Ecosystem**: Powered by Rsbuild, Rslib benefits from a lightweight plugin system and a collection of high-quality official plugins. Furthermore, Rsbuild's compatibility with most webpack plugins and all Rspack plugins allows library developers to seamlessly integrate existing community or in-house plugins into their library projects.
+
 ## 🎯 Ecosystem
 
 Rslib is implemented based on Rsbuild and fully reuses the capabilities and ecology of Rsbuild.
 
-The following diagram illustrates the relationship between Rsbuild and other tools in the ecosystem:
+The following diagram illustrates the relationship between Rslib and other tools in the ecosystem:
 
 ![Rspack stack layers](https://assets.rspack.dev/rsbuild/assets/rspack-stack-layers.png)