add dev guide for constraint layout.

        value: 順応性のある UI フローの実装

      - name: zh-cn-lang

        value: 实施自适应用户界面流程

  - title: Build a Responsive UI with ConstraintLayout

    path: /training/constraint-layout/index.html

    path_attributes:

    - name: description

      value: How to build a layout using ConstraintLayout and the Android Studio Layout Editor.

  - title: Adding the App Bar

    path: /training/appbar/index.html

    path_attributes: