Fix the code to print all events in a catalog

[seisman]

There are two different ways to print all events in a catalog:

1. print(cat.__str__(print_all=True))

2. for event in cat:
      print(event)

ObsPy recommends the first option, but I don't like due to the following two reasons:

1. As shown in the screenshot below, the first option doesn't display well in the side note (a missing bracket at the end).
2. The first option is not easy to remember, and the second option is much easier to understand and remember.

[github-actions[bot]]

This comment was written by the Continuous Documentation bot!

• Preview: https://seismo-learn.org/sitepreview/seismo-learn/seismology101/fix-print-catalog/index.html
• Commit hash: 1bfcf83c1c70e36bbd05a3e69fedebae2d793246