gksudo gedit /usr/share/applications/postman.desktop
or
sudo gedit /usr/share/applications/postman.desktop
**Note gksudo is used for graphical sudo
and put this in the file
[Desktop Entry]
Encoding=UTF-8
Version=1.0
Type=Application
Name=Postman
Icon=postman.png
Path=/home/[your username]/Postman
Exec=/home/[your username]/Postman/Postman
StartupNotify=false
StartupWMClass=Postman
OnlyShowIn=Unity;GNOME;
X-UnityGenerated=true
and then Save
That's the same for any app. we want to put it's icon in launcher. ;)