Docs: update README.md

I added descriptions about `plugin:node/recommended`.

Author: mysticatea

README.md

@@ -18,37 +18,36 @@ Additional ESLint's rules for Node.js
 
 ```json
 {
-    "extends": "eslint:recommended",
     "plugins": ["node"],
-    "env": {
-        "es6": true,
-        "node": true
-    },
-    "rules": {
-        "node/no-deprecated-api": "error",
-        "node/no-missing-import": "error",
-        "node/no-missing-require": "error",
-        "node/no-unpublished-import": "error",
-        "node/no-unpublished-require": "error",
-        "node/no-unsupported-features": ["error", {"version": 4}],
-        "node/process-exit-as-throw": "error",
-        "node/shebang": "error"
-    }
+    "extends": ["eslint:recommended", "plugin:node/recommended"]
 }
 ```
 
+## Configs
+
+This plugin provides `plugin:node/recommended` preset config.
+This preset config:
+
+- enables the environment of ES2015 (ES6) and Node.js.
+- enables rules which are given :star: in the following table.
+
+**Note:** It recommends a use of [the "engines" field of package.json](https://docs.npmjs.com/files/package.json#engines). The "engines" field is used by [no-unsupported-features](docs/rules/no-unsupported-features.md) rule.
+
 ## Rules
 
-Some rules are slow because it searches `package.json` and opens it.
+|        |          | Rule ID                                                          | Description |
+|:------:|:--------:|:-----------------------------------------------------------------|:------------|
+| :star: |          | [no-deprecated-api](docs/rules/no-deprecated-api.md)             | Disallow deprecated API.
+|        |          | [no-missing-import](docs/rules/no-missing-import.md)             | Disallow `import` and `export` declarations for files that don't exist.
+| :star: |          | [no-missing-require](docs/rules/no-missing-require.md)           | Disallow `require()`s for files that don't exist.
+|        |          | [no-unpublished-import](docs/rules/no-unpublished-import.md)     | Disallow `import` and `export` declarations for files that are not published.
+| :star: |          | [no-unpublished-require](docs/rules/no-unpublished-require.md)   | Disallow `require()`s for files that are not published.
+| :star: |          | [no-unsupported-features](docs/rules/no-unsupported-features.md) | Disallow unsupported ECMAScript features on the specified version.
+|        |          | [process-exit-as-throw](docs/rules/process-exit-as-throw.md)     | Make the same code path as throw at `process.exit()`. (⚠ Experimental)
+| :star: | :pencil: | [shebang](docs/rules/shebang.md)                                 | Suggest correct usage of shebang.
 
-- [no-deprecated-api](docs/rules/no-deprecated-api.md) - Disallow deprecated API.
-- [no-missing-import](docs/rules/no-missing-import.md) - Disallow `import` and `export` declarations for files that don't exist.
-- [no-missing-require](docs/rules/no-missing-require.md) - Disallow `require()`s for files that don't exist.
-- [no-unpublished-import](docs/rules/no-unpublished-import.md) - Disallow `import` and `export` declarations for files that are not published.
-- [no-unpublished-require](docs/rules/no-unpublished-require.md) - Disallow `require()`s for files that are not published.
-- [no-unsupported-features](docs/rules/no-unsupported-features.md) - Disallow unsupported ECMAScript features on the specified version.
-- [process-exit-as-throw](docs/rules/process-exit-as-throw.md) - Make the same code path as throw at `process.exit()`. (⚠ Experimental)
-- [shebang](docs/rules/shebang.md) - Suggest correct usage of shebang. (fixable)
+- :star: - the mark of a recommended rule.
+- :pencil: - the mark of a fixable rule.
 
 ## Semantic Versioning Policy