fix: correct indentation for YAML rules in README.template and readme.dart

Author: mcquenji

README.template

@@ -10,7 +10,7 @@ To use the recommended lint rules drop the following into your `analysis_options
 plugins:
   grumpy_lints:
     diagnostics:
-{{yaml_rules(4)}}
+{{yaml_rules(3)}}
 ```
 
 

bin/readme.dart

@@ -71,7 +71,7 @@ void main(List<String> args) {
 
   final yamlMatch = yamlRulesRegex.firstMatch(template)!;
 
-  final indent = '  ' * int.parse(match.group(1) ?? '0');
+  final indent = '  ' * int.parse(yamlMatch.group(1) ?? '0');
 
   final yamlRules = rules.map((r) => '$indent${r.name}: true').join('\n');