improve accuracy of introtutorial.rst coordinates

[wholmgren]

It might be a good time to correct the inaccurate coordinates in introtutorial.rst.
Right now, San Francisco is in Reno and Berlin is almost in France.

If you're interested:

     import pandas as pd
     import matplotlib.pyplot as plt
 
-    # very approximate
     # latitude, longitude, name, altitude, timezone
     coordinates = [
-        (30, -110, 'Tucson', 700, 'Etc/GMT+7'),
-        (35, -105, 'Albuquerque', 1500, 'Etc/GMT+7'),
-        (40, -120, 'San Francisco', 10, 'Etc/GMT+8'),
-        (50, 10, 'Berlin', 34, 'Etc/GMT-1'),
+        (32.2, -111.0, 'Tucson', 700, 'Etc/GMT+7'),
+        (35.1, -106.6, 'Albuquerque', 1500, 'Etc/GMT+7'),
+        (37.8, -122.4, 'San Francisco', 10, 'Etc/GMT+8'),
+        (52.5, 13.4, 'Berlin', 34, 'Etc/GMT-1'),
     ]

Here's the commit:
https://github.com/EricDuminil/pvlib-python/commit/7abbfc8e7d9c4a59ee1b937948cb4eefeaab1801

Originally posted by @EricDuminil in #1144 (comment)

[EricDuminil]

Is there something specific I could help with?
Show on a map where the coordinates where, and where they are now?

[wholmgren]

It would help if you made a pull request with the changes you'd like to see