Update generateScopedName type in documentation

Author: pascalduez

README.md

@@ -203,7 +203,7 @@ Provides the full list of PostCSS plugins to the pipeline. Providing this cancel
 
 Short alias for the [postcss-modules-extract-imports](https://github.com/css-modules/postcss-modules-extract-imports) plugin's `createImportedName` option.
 
-### `generateScopedName` function
+### `generateScopedName` string|function
 
 Short alias for the [postcss-modules-scope](https://github.com/css-modules/postcss-modules-scope) plugin's option. Helps you to specify the custom way to build generic names for the class selectors.
 You may also use a string pattern similar to the webpack's [css-loader](https://github.com/webpack/css-loader#local-scope).