[DOC] Update code snippet in feathr-concepts-for-beginners document.

[loomlike]

Willingness to contribute

Yes. I would be willing to contribute to this for with guidance from the Feathr community.

URL(s) with the issue

https://github.com/feathr-ai/feathr/blob/main/docs/concepts/feathr-concepts-for-beginners.md

Description of proposal (what needs changing)

The code snippet is showing NYC taxi fare examples, but the description is about fraud detection example.
Those two need to be aligned.