Change step with new_cop command for rubocop-rspec

before:
```
Do 4 steps:
  1. Modify the description of RSpec/CopName in config/default.yml
  2. Implement your new cop in the generated file!
  3. Commit your new cop with a message such as
     e.g. "Add new `RSpec/CopName` cop"
  4. Run `bundle exec rake changelog:new` to generate a changelog entry
```

after:
```
Do 4 steps:
  1. Modify the description of RSpec/CopName in config/default.yml
  2. Implement your new cop in the generated file!
  3. Add an entry about new cop to CHANGELOG.md
  4. Commit your new cop with a message such as
     e.g. "Add new `RSpec/CopName` cop"
```

Author: ydah

Rakefile

@@ -90,13 +90,14 @@ task default: %i[build_config spec
 desc 'Generate a new cop template'
 task :new_cop, [:cop] do |_task, args|
   require 'rubocop'
+  require_relative 'lib/rubocop/rspec/cop/generator'
 
   cop_name = args.fetch(:cop) do
     warn "usage: bundle exec rake 'new_cop[Department/Name]'"
     exit!
   end
 
-  generator = RuboCop::Cop::Generator.new(cop_name)
+  generator = RuboCop::RSpec::Cop::Generator.new(cop_name)
   generator.write_source
   generator.write_spec
   generator.inject_require(root_file_path: 'lib/rubocop/cop/rspec_cops.rb')

lib/rubocop/rspec/cop/generator.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module RSpec
+    module Cop
+      # Source and spec generator for new cops
+      #
+      # This generator will take a cop name and generate a source file
+      # and spec file when given a valid qualified cop name.
+      # @api private
+      class Generator < RuboCop::Cop::Generator
+        def todo
+          <<~TODO
+            Do 4 steps:
+              1. Modify the description of #{badge} in config/default.yml
+              2. Implement your new cop in the generated file!
+              3. Add an entry about new cop to CHANGELOG.md
+              4. Commit your new cop with a message such as
+                 e.g. "Add new `#{badge}` cop"
+          TODO
+        end
+      end
+    end
+  end
+end