Content request: Use the specutils generic Table reader to load a spectrum

[kakirastern]

To follow up on a thread from the Learn Astropy session during the Spectroscopy Sprint 2020 as suggested by @eblur. To write a tutorial notebook for guiding the user to load/read a spectrum with the specutils generic Table loader/reader.

Another idea: To generalize to the case of using the custom loader/reader as well, to cover both the generic and custom types.

Starting point: specutils docs