Add introduction to seismogram

[core-man]

#6

[github-actions]

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• Preview: https://seismo-learn.org/sitepreview/seismo-learn/seismology101/add-introduction-to-seismic-data
• Commit hash: 10f4dac

[seisman]

https://seismo-learn.org/sitepreview/seismo-learn/seismology101/add-introduction-to-seismic-data/seismogram/

This page is empty. Do you want to move the introduction part to the index.rst file, so they will be shown in this page?

[core-man]

https://seismo-learn.org/sitepreview/seismo-learn/seismology101/add-introduction-to-seismic-data/seismogram/

This page is empty. Do you want to move the introduction part to the index.rst file, so they will be shown in this page?

Okay.