[doc] n3fit model

[vschutze-alt]

Document n3fit model.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.13%. Comparing base (47028b9) to head (8cdffd8).
⚠️ Report is 69 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #437      +/-   ##
==========================================
+ Coverage   95.02%   96.13%   +1.10%     
==========================================
  Files          31       31              
  Lines        1648     1654       +6     
==========================================
+ Hits         1566     1590      +24     
+ Misses         82       64      -18     

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[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 0 complexity · 0 duplication

Metric	Results
Complexity	0
Duplication	0

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[vschutze-alt]

We should add the instruction to do the "export jax tensor flow" command before fitting

[ecole41]

We should add the instruction to do the "export jax tensor flow" command before fitting

@NinaElmer Has re-tested the instructions on the branch and this now works 'out of the box' so this is not needed