docs(bezier-tokens): apply changes from #1766 (#1768)

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## Summary
<!-- Please brief explanation of the changes made -->

#1766 의 변경사항을 README에도 적용합니다.

Author: sungik-choi

packages/bezier-tokens/README.md

@@ -17,8 +17,8 @@ You can access and use values by token group.
 ```ts
 import { tokens } from '@channel.io/bezier-tokens'
 
-console.log(tokens.global['blue-300']) // "#..."
-console.log(tokens.lightTheme['bg-black-dark']) // "#..."
+console.log(tokens.global.color['blue-300']) // "#..."
+console.log(tokens.lightTheme.color['bg-black-dark']) // "#..."
 ```
 
 ### CSS