I followed the steps in the Qxt User Guide and when I try

#include <QxtBlowfish>

the compiler cannot find the directory.

Here what I did to install

The user guide stated:
Make sure qmake is in your PATH and run (How do I make sure qmake is in my PATH? how to check?)

Step1: ./configure
Step2: make && make install
Step3: Add the following lines to my .pro file:

CONFIG += qxt
QXT += core gui