Could not find a package configuration file provided by "Qt5Widgets"

edit

I am using indigo in ubuntu14.04.2 following this. I did like this:

$ mkdir -p ~/overlay_ws
$ cd ~/overlay_ws
$ mkdir -p ~/overlay_ws/src
$ cd ~/overlay_ws/src
$ wstool init

then added a ros package

$ wstool set ros_tutorials --git git://github.com/ros/ros_tutorials.git
$ wstool update

build it

$ source /opt/ros/groovy/setup.bash
$ cd ~/overlay_ws/
$ catkin_make

error occured:

-- Using these message generators: gencpp;genlisp;genpy
CMake Error at ros_tutorials/turtlesim/CMakeLists.txt:6 (find_package):
  By not providing "FindQt5Widgets.cmake" in CMAKE_MODULE_PATH this project
  has asked CMake to find a package configuration file provided by
  "Qt5Widgets", but CMake did not find one.

  Could not find a package configuration file provided by "Qt5Widgets" with
  any of the following names:

    Qt5WidgetsConfig.cmake
    qt5widgets-config.cmake

  Add the installation prefix of "Qt5Widgets" to CMAKE_PREFIX_PATH or set
  "Qt5Widgets_DIR" to a directory containing one of the above files.  If
  "Qt5Widgets" provides a separate development package or SDK, be sure it has
  been installed.

my questions is : 1 What's the relationship between ROS and the Qt5 ?

2 Should I install Qt5 in my PC ? thanks.