Fix README code snippet.

Looking at the README in the PyCharm IDE, discovered that it incorrectly
referenced `print_prog_score`.  This is not a function, but a method on
`Settings`.

Author: rpgoldman

README.md

@@ -159,11 +159,11 @@ You can download and compile these solvers from the [MaxSAT 2023 evaluation](htt
 You can import Popper and use it in your Python code like so:
 
 ```python
-from popper.util import Settings, print_prog_score
+from popper.util import Settings
 from popper.loop import learn_solution
 
 settings = Settings(kbpath='input_dir')
 prog, score, stats = learn_solution(settings)
 if prog != None:
-    print_prog_score(prog, score)
+    settings.print_prog_score(prog, score)
 ```