Update Docs for VMEC Input File Conversion

[dpanici]

Note to update the docs for the input file converter for VMEC to DESC, specifically to say that it will now include default continuation per #246 , and update the converted input file to reflect this as well

[dpanici]

Also add .lower() to words[0] inside of input_reader.py to handle input args that are just different cases (like ANSI instead of ansi)

or change the 00 tutorial to not list ANSI and Fringe as examples of how to set the spectral_indexing option

[dpanici]

#261 addresses these

[unalmis]

The notebooks needed modification to run in #251 . I updated the 00 tutorial substantially as DESC now does automatic continuation on vmec input file conversion. Feel free to change it of course.