docs: add check-unnecessary-nullable to readme

Author: incendial

README.md

@@ -36,6 +36,7 @@ Dart Code Metrics is a static analysis tool that helps you analyse and improve y
 - Checks for [anti-patterns](https://dartcodemetrics.dev/docs/anti-patterns/overview)
 - Checks [unused `*.dart` files](https://dartcodemetrics.dev/docs/cli/check-unused-files)
 - Checks [unused l10n](https://dartcodemetrics.dev/docs/cli/check-unused-l10n)
+- Checks [unnecessary nullable parameters](https://dartcodemetrics.dev/docs/cli/check-unnecessary-nullable)
 - Can be used as [CLI](https://dartcodemetrics.dev/docs/cli/overview), [analyzer plugin](https://dartcodemetrics.dev/docs/analyzer-plugin) or [library](https://dartcodemetrics.dev/docs/getting-started/installation#library)
 
 ## Links
@@ -119,6 +120,7 @@ The package can be used as CLI and supports multiple commands:
 | Command            | Example of use                                            | Short description                                         |
 | ------------------ | --------------------------------------------------------- | --------------------------------------------------------- |
 | analyze            | dart run dart_code_metrics:metrics analyze lib            | Reports code metrics, rules and anti-patterns violations. |
+| check-unnecessary-nullable | dart run dart_code_metrics:metrics check-unnecessary-nullable lib | Checks unnecessary nullable parameters in functions, methods, constructors. |
 | check-unused-files | dart run dart_code_metrics:metrics check-unused-files lib | Checks unused \*.dart files.                              |
 | check-unused-l10n  | dart run dart_code_metrics:metrics check-unused-l10n lib  | Check unused localization in \*.dart files.               |
 | check-unused-code  | dart run dart_code_metrics:metrics check-unused-code lib  | Checks unused code in \*.dart files.                      |
@@ -150,6 +152,26 @@ Console report example:
 
 ![Console report example](https://raw.githubusercontent.com/dart-code-checker/dart-code-metrics/master/assets/analyze-console-report.png)
 
+#### Check unnecessary nullable parameters
+
+Checks unnecessary nullable parameters in functions, methods, constructors. To execute the command, run
+
+```sh
+$ dart run dart_code_metrics:metrics check-unnecessary-nullable lib
+
+# or for a Flutter package
+$ flutter pub run dart_code_metrics:metrics check-unnecessary-nullable lib
+```
+
+It will produce a result in one of the format:
+
+- Console
+- JSON
+
+Console report example:
+
+![Console report example](https://raw.githubusercontent.com/dart-code-checker/dart-code-metrics/master/assets/unused-files-console-report.png)
+
 #### Check unused files
 
 Checks unused `*.dart` files. To execute the command, run

assets/unnecessary-nullable-console-report.png

@@ -1,6 +1,6 @@
 # Check unnecessary nullable parameters
 
-Check unnecessary nullable parameters in functions, methods, constructors. Removing unnecessary nullables can help reduce amount of checks in the code.
+Checks unnecessary nullable parameters in functions, methods, constructors. Removing unnecessary nullables can help reduce amount of checks in the code.
 
 To execute the command, run