feat: Add documentation for renaming style rules

This commit introduces a new section in the README that explains how to
rename style rules by query selector. It includes examples of CSS and
Svelte code, and shows how the code gets converted after renaming.

Author: ryoppippi

README.md

@@ -83,5 +83,41 @@ div { color: green; }
 </style>
 ```
 
+### Rename Style Rules by Query Selector
+
+You can rename style rules by query selector.
+
+For example, the following CSS and Svelte:
+
+```css
+/* a.css */
+
+div { color: red; }
+
+.m0 { color: blue; }
+```
+
+```svelte
+<p class="m1"> world </p>
+
+<style>
+@import "./a.css?.m0=.m1" scoped;
+
+div { color: green; }
+</style>
+```
+
+will get converted into:
+
+```svelte
+<p class="m1"> world </p>
+
+<style>
+.m1 { color: blue; }
+
+div { color: green; }
+</style>
+```
+
 ## License
 [MIT](./LICENSE)