Minor Documentation and Typo Fixes

[leopardracer]

Description:
This pull request makes minor improvements to the documentation and references in the codebase:

• Updates the docstring in pvlib/bifacial/pvfactors.py for clarity regarding the use of external implementations.
• Fixes a typo ("Parametres" → "Parameters") in a reference within pvlib/ivtools/sdm/_fit_desoto_pvsyst_sandia.py.

No functional code changes are included; these are documentation and text corrections only.