File formats documentation

[AlexandreDubray]

Hello,

Unless I missed that part, it seems that there is no documentation (or pointers to external resources) on the formats supported to read probabilistic circuits from a file.
Altought the respective parser files gives a good idea on what is expected, it would be more practical (and beginner friendly !) to have a dedicated section in the documentation that explain how to format a file to represent a probabilistic circuits (or pointers to external resources for formats like psdd or spn).

[khosravipasha]

The main formtat we use right now is using .jpc format. When you save a circuit to file it add a comment on top on how the file is formatted so you can check there.

We can also add that in the documentation website somewhere. We don't have any timelines on these changes, would be happy to accept a PR though.

https://github.com/Juice-jl/ProbabilisticCircuits.jl/blob/e531bb0804009990635509c8cae6d89e21cda7b7/src/io/jpc_io.jl#L159-L171