NDCG and Confusion Matrix Examples

Create a usage example on how these ranking metrics can be used:

```
+------------------------------------------------------------+-------------------------------------------------------------------------------+
| Python API | Description |
+============================================================+===============================================================================+
| `metriks.ndcg(y_true, y_prob, k)` | A score for measuring the quality of a set of ranked results. |
+------------------------------------------------------------+-------------------------------------------------------------------------------+
| `metriks.confusion_matrix_at_k(y_true, y_prob, k)` | Generates binary predictions from probabilities by evaluating the top k |
| | items (in ranked order by y_prob) as true. |
+------------------------------------------------------------+-------------------------------------------------------------------------------+
```

1. Identify a dataset that can be used to train a ranking model
2. Train a ranking model with the data
3. Use the given metrics above and show results and demonstrate how these metrics can be used