DOC: clarify GroupBy iteration example

[veerasai06]

Summary

This pull request enhances the Pandas documentation by improving the explanation of how to iterate over a GroupBy object in the user guide.
The previous description was brief and slightly unclear for new contributors and users learning group operations.
The updated section clearly explains that iteration yields (key, group) pairs and provides a concise example to illustrate this behavior.

What Was Changed

• Edited doc/source/user_guide/groupby.rst
• Replaced the vague sentence “The groupby object can be iterated like (key, value)”
  with a clearer explanation describing (key, group) pairs.
• Added an easy-to-understand code example showing practical iteration.

Why This Change Matters

This clarification helps readers quickly understand the structure returned during iteration,
making the documentation more beginner-friendly and accurate.
It aligns with Pandas’ goal of maintaining precise, example-driven documentation.

• closes #xxxx (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

[mroeschke]

Thanks for the pull request, but given the lack of linked issue and AI generated summary I cannot clearly understand the intent of this PR so closing