Following are the required steps for installation and addition of QWT library to QT.

Steps

Download qwt-6.1.3 from here.
Open terminal and run sudo apt-get update.
sudo apt-get upgrade.
sudo rpi-update (for raspberry pi).
sudo apt-get install qt5-default.
sudo apt-get install qtcreator.
sudo apt-get install libqt5svg5*
sudo apt-get install qttools5-dev.
cd qwt-6.1.3 (go to qwt-6.1.3 directory).
qmake qwt.pro
make
sudo make install
cd /usr/local/qwt-6.1.3/plugins/designer (go to designer directory via the path given)
sudo cp libqwtdesignerplugin.so /usr/lib/arm-linux-gnueabihf/qt5/plugins/designer
Run qmake -set QMAKEFEATURES /usr/local/qwt-6.1.3/features in terminal
cd /qwt-6.1.3/examples
qmake
make
cd /etc/ld.so.conf.d/
sudo nano qwt.conf
paste /usr/local/qwt-6.1.3/lib in the edit textbox.
sudo ldconfig
ldconfig -p | grep qwt
cd /qwt-6.1.3/examples/bin/
./oscilloscope
Open qt creator->new project
Add CONFIG += qwt in .pro file
If needed add INCLUDEPATH += /usr/local/qwt-5.2.1/include in .pro file
If needed add LIBS += -L/usr/local/qwt-5.2.1/lib -lqwt in .pro file
All set now.