Add cucumber scenario for layout CLI option

features/cli/layout.feature

@@ -0,0 +1,11 @@
+Feature: layout CLI option
+
+  Scenario: specifies the layout class
+    Given a file named layout.rb with:
+      """
+      class MyLayout
+        def register _; end
+      end
+      """
+    When I run uhwm with option -v -r./layout -l MyLayout
+    Then the output must match /layout.+mylayout/i