Documentation: Link to SAM CSV weather file format is broken

[williamhobbs]

This reference link for SAM CSV file format in this documentation page, https://pvlib-python.readthedocs.io/en/stable/generated/pvlib.iotools.read_psm3.html, appears broken:

This link might be acceptable: https://sam.nrel.gov/images/web_page_files/sam-help-2020-2-29-r1_weather_file_formats.pdf

[kandersolar]

That PDF likes to disappear. In the meantime, NREL/developer.nrel.gov#196 has a link to a copy on the internet archive.