Since I don't want to write: "export LD_LIBRARY_PATH=<path to sfml>/lib && ./sfml-app" into my terminal every time i want to run sfml-app, I did this:
1 Start gedit (go to terminal and type "gedit" then enter)
2 Write:
#!/bin/sh
export LD_LIBRARY_PATH=<path to sfml>/lib && ./sfml-app
3 Save in the same directory as sfml-app.