Fix in ModelChain effective_irradiance methods by adding examples

[Chirag3841]

• Closes Run ModelChain from POA irradiance #943 (documentation portion: adds examples to run_model_from_effective_irradiance)
• I am familiar with the contributing guidelines
• Tests added (not required for documentation-only PR)
• Updates entries in docs/sphinx/source/reference (not required — API unchanged)
• Adds description and name entries in the "what's new" file (not required for minor doc updates)
• New code is fully documented (docstrings updated with numpydoc-compliant examples)
• Pull request is nearly complete and ready for detailed review
• Maintainer: add labels and milestone

Address the documentation portion of #943
This pull request improves the documentation for
ModelChain.run_model_from_effective_irradiance() by adding a complete, runnable example to the
docstring.
Changes demonstrates-
1)Providing effective irradiance as the primary model input
 Shows how users can bypass POA and spectral steps when effective irradiance is already calculated.

2)Creating a minimal DataFrame containing:
 • effective_irradiance (required)
 • temp_air and wind_speed (optional weather inputs)

3)Running the model using run_model_from_effective_irradiance
 Illustrates how ModelChain handles temperature, DC, and AC modeling starting from effective irradiance.

4)Ensuring formatting and indentation follow pvlib’s numpydoc standards
 Docstring follows pvlib conventions:
 • Examples block
 • Proper indentation
 • Consistent parameter formatting
 • Clear Notes section
 @cwhanse I have done the changes for PR3.

[Chirag3841]

@cwhanse
I have done changes in run_model_effective_irradiance() method by adding example.

[cwhanse]

@Chirag3841 this PR is also stacked on top of #2601. Please rebase on to pvlib's main.

[Chirag3841]

@cwhanse
Changes applied. Please review.