Fix syntax highlighting on readthedocs

[cchwala]

• [x] closes #22
• [x] Tests added and passed if fixing a bug or adding a new feature
• [x] All code checks from pre-commit passed
• [x] Added an entry in the CHANGELOG.md file

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (61c4063) 100.00% compared to head (4593188) 100.00%. Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #23 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 3 3 Lines 43 43 ========================================= Hits 43 43 ```

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[cchwala]

Syntax highlighting works now, see https://poligrain--23.org.readthedocs.build/en/23/notebooks/Calculate_distances.html