Filename in Tutorial->simulations

[EGaraldi]

The code snippet and sample outputs in the simulation tutorial do not match the one obtained following the link provided in the same page. The former is "TNG50-4_snapshot" while the latter is "snapdir_030". Similarly, the content of the file is slightly different than showed in the tutorial page. If possible, homogenize them for clarity.

[dnelson86]

I suggest to drop non-standard names like "TNG50-4_snapshot" completely.

Let's stick to the data formats, and organization, of the large data sets, as they are available.

(If this means that e.g. any automatic testing based on such snapshots must run with access to /virgotng/ or similar, I think this is ok).

[kyleaoman]

Just to be specific, the "GFM_AGNRadiation" field mentioned in the tutorial doesn't exist in the example file.

[kyleaoman]

Likewise the projection image from the example file differs a bit from the one in the documentation.

[cbyrohl]

Thanks @EGaraldi, non standard name dropped in favor of folder name "snapdir_030" in #126 . Thanks @kyleaoman, field reference and projection image adjusted in #114