DOC: Add example for making Excel headers bold using Styler

[antznette1]

@rhshadrach

This PR adds a documentation example showing how to make Excel header rows bold when
exporting DataFrames using Styler.applymap_index().

This addresses a common use case mentioned in issue #62651 where users want
to bold header rows in Excel exports. The example demonstrates the recommended
approach using Styler rather than modifying to_excel() directly.

Example:

df.style.applymap_index(lambda v: "font-weight: bold;", axis="columns").to_excel("out.xlsx")

Related to #62651

[antznette1]

Hi @rhshadrach, I hope you’re doing well.
When you get a chance, could you please review my PR? I’d really appreciate your feedback so we can move it forward.
Thanks a lot!

[rhshadrach]

Thanks for the PR. Currently the user guide has all docs on the styler in styler.ipynb, and where there is an operation like to_excel that is relevant to the styler, we link instead of spreading out or duplicating the documentation. I think we should stick to this pattern.

The documentation being added here also seems duplicate the documentation here:

https://pandas.pydata.org/pandas-docs/dev/user_guide/style.html#Acting-on-the-Index-and-Column-Headers

applymap_index is not mentioned because it has been removed.

[antznette1]

Thanks for the PR. Currently the user guide has all docs on the styler in styler.ipynb, and where there is an operation like to_excel that is relevant to the styler, we link instead of spreading out or duplicating the documentation. I think we should stick to this pattern.

The documentation being added here also seems duplicate the documentation here:

https://pandas.pydata.org/pandas-docs/dev/user_guide/style.html#Acting-on-the-Index-and-Column-Headers

applymap_index is not mentioned because it has been removed.

Thank you for the feedback.
I see the functionality is already documented in io.rst (with an example using font-weight: bold) and links to the styler documentation. I also missed that applymap_index has been removed.
I’ll close this PR. Apologies for the oversight.