Add system generator feature

Author: vivekmiyani

features/generator_specs/system_specs.feature

@@ -0,0 +1,21 @@
+Feature: System generator spec
+
+    Scenario: System generator
+        When I run `bundle exec rails generate rspec:system posts`
+        Then the features should pass
+        Then the output should contain:
+          """
+                create  spec/system/posts_spec.rb
+          """
+
+    Scenario: System generator with customized `default-path`
+        Given a file named ".rspec" with:
+          """
+          --default-path behaviour
+          """
+        And I run `bundle exec rails generate rspec:system posts`
+        Then the features should pass
+        Then the output should contain:
+          """
+                create  behaviour/system/posts_spec.rb
+          """