fix: add readme for css hash length

Author: denisx

README.md

@@ -1348,6 +1348,47 @@ import styles from 'Component.module.scss';
 ctx.fillStyle = `${svars.colorBackgroundCanvas}`;
 ```
 
+### Plugin: One Letter CSS (with hash length check)
+
+For efficient gzip/br compression, plugin combine css hash via one symbol name,
+as a classname position at file, with filepath `hash:base64:8`, to have strong sequences
+
+**webpack.config.js**
+
+```js
+const { OneLetterCss } = require('css-loader/plugins');
+const MyOneLetterCss = new OneLetterCss();
+
+const cssHashLen = 8;
+
+module.exports = {
+  module: {
+    rules: [
+      {
+        test: /\.css$/i,
+        loader: 'css-loader',
+        options: {
+          modules: {
+            mode: 'local',
+            localIdentName: `[hash:base64:${cssHashLen}]`,
+            // for develop
+            // localIdentName: `[local]__[hash:base64:${cssHashLen}]`,
+            getLocalIdent: MyOneLetterCss.getLocalIdent,
+          },
+        },
+      },
+    ],
+  },
+  plugins: [
+    ...plugins,
+    new HashLenSuggest({
+      instance: MyOneLetterCss,
+      selectedHashLen: cssHashLen,
+    }),
+  ],
+};
+```
+
 ## Contributing
 
 Please take a moment to read our contributing guidelines if you haven't yet done so.