[Improvement] Adds scores to the example provided in the readme.md

[miguelgondu]

To give the user some peace of mind after running the example provided under ## Usage, we could include the scores the user is expected to see.

In other words, we change the provided example to:

from molskill.scorer import MolSkillScorer

smiles_strs = ["CCO", "O=C(Oc1ccccc1C(=O)O)C"] 

scorer = MolSkillScorer()
scores = scorer.score(smiles_strs)  # [ 19.531034 -11.309371]