docs: added windows specfic intructions for building documentation

[Troppy2]

Fixes #1491

Added Windows-specific instructions for building documentation:

• Note to use make html instead of make docs
• Clarify that requirements-docs.txt needs to be installed

This helps Windows users who may not be familiar with the Unix make commands.

[snowman2]

Suggested change

	**On Windows:** Use ``make html`` instead of ``make docs``. Also ensure you have installed the documentation requirements with ``pip install -r requirements-docs.txt`` before building.
	**On Windows:** Use ``make -C docs html`` instead of ``make docs``. Also ensure you have installed the documentation requirements with ``pip install --group docs`` before building.

[snowman2]

#1602