fix documentation home page title

[wholmgren]

Describe the bug
the pvlib documentation home page is titled "Citing pvlib python"

To Reproduce
go to the documentation home page https://pvlib-python.readthedocs.io/en/stable/ and look at the page title.

Expected behavior
just "pvlib python" or maybe "pvlib python: A set of documented functions for simulating the performance of photovoltaic energy systems."

Screenshots

Versions:

• pvlib.__version__: 0.7.1

Additional context
probably needs a new sphinx header