fix: change config name

Author: shixin-guo

README.md

@@ -80,9 +80,9 @@ If unspecified, no artifact will be created.
 
 Default: `''` (no artifact)
 
-### `customize_file_colors`
+### `file_colors`
 
-User can customize color of file. need to be a Json String. it will replace the key-value pair of [src/language-colors.json].
+You can customize the colors for specific file extensions. Key/value pairs will extend the [default colors](https://github.com/githubocto/repo-visualizer/pull/src/language-colors.json).
 
 For example: '{"js": "red","ts": "green"}'
 default: '{}'