Provide in each Notebook details on the used data

[jgieseler]

Provide in each Notebook details on the used data at the very end. In https://github.com/soler-he/sep_tools/blob/main/SEP_Multi-Spacecraft-Plot.ipynb this has already been done, but the data is not necessarily the same in each Notebook.

• SEP_Fluence-Spectra.ipynb
• SEP_Multi-Instrument-Plot.ipynb
• SEP_Multi-Spacecraft-Plot.ipynb
• SEP_PADs-and-Anisotropy.ipynb
• SEP_PyOnset.ipynb
• SEP_Regression-Onset.ipynb