docs: update README

README.md

@@ -10,12 +10,21 @@ An Rsbuild plugin to integrate with [Tailwind CSS](https://tailwindcss.com/) V3.
   <a href="https://npmcharts.com/compare/rsbuild-plugin-tailwindcss?minimal=true"><img src="https://img.shields.io/npm/dm/rsbuild-plugin-tailwindcss.svg?style=flat-square&colorA=564341&colorB=EDED91" alt="downloads" /></a>
 </p>
 
+## Why?
+
+Tailwind CSS is able to remove unused CSS classes through [Content Configuration](https://tailwindcss.com/docs/content-configuration). However, its accuracy may be insufficient when:
+
+- Using multiple entries
+- Using a Tailwind CSS-based component library
+
+This plugin uses the Rspack module graph to override the `content` configuration with imported modules, generating Tailwind CSS output _**based on usage**_.
+
 ## Usage
 
 Install:
 
 ```bash
-npm add rsbuild-plugin-tailwindcss -D
+npm add tailwindcss@3 rsbuild-plugin-tailwindcss -D
 ```
 
 Add plugin to your `rsbuild.config.ts`:
@@ -29,6 +38,84 @@ export default {
 };
 ```
 
+### Custom Tailwind CSS Configuration
+
+Create a `tailwind.config.js` file at the root of the project:
+
+```js
+/** @type {import('tailwindcss').Config} */
+export default {
+  theme: {
+    colors: {
+      blue: "#1fb6ff",
+      purple: "#7e5bef",
+      pink: "#ff49db",
+      orange: "#ff7849",
+      green: "#13ce66",
+      yellow: "#ffc82c",
+      "gray-dark": "#273444",
+      gray: "#8492a6",
+      "gray-light": "#d3dce6",
+    },
+  },
+};
+```
+
+This will be auto-loaded by Rsbuild and applied by `rsbuild-plugin-tailwindcss`.
+
+> [!NOTE]
+>
+> You don't need to add `content` in the `tailwind.config.js`. `rsbuild-plugin-tailwindcss` will add the imported modules for you.
+
+### Custom PostCSS Options
+
+Create a `postcss.config.js` file at the root of the project:
+
+```js
+export default {
+  plugins: {
+    cssnano: process.env["NODE_ENV"] === "production" ? {} : false,
+  },
+};
+```
+
+> [!NOTE]
+>
+> You don't need to add `tailwindcss` in the `postcss.config.js`. `rsbuild-plugin-tailwindcss` will add the plugin for you.
+
+Or use the [`tools.postcss`](https://rsbuild.dev/config/tools/postcss) option in `rsbuild.config.ts`.
+
+## Options
+
+### `config`
+
+- Type: `string | undefined`
+- Default: `tailwind.config.js`
+
+The path to custom Tailwind CSS configuration. Could be a relative path from the root of the project or an absolute path.
+
+- Example:
+
+```js
+// rsbuild.config.ts
+import { pluginTailwindCSS } from "rsbuild-plugin-tailwindcss";
+
+export default {
+  plugins: [
+    pluginTailwindCSS({
+      config: "./config/tailwind.config.js",
+    }),
+  ],
+};
+```
+
+## Credits
+
+Thanks to:
+
+- [Tailwind CSS V4](https://tailwindcss.com/blog/tailwindcss-v4-alpha) for the idea of purge CSS by module graph.
+- The [purge-tailwind-plugin](https://github.com/hardfist/purge-tailwind-plugin) created by [@hardfist](https://github.com/hardfist) for the implementation of the Rspack plugin.
+
 ## License
 
 [MIT](./LICENSE).