Fix docstring

[ericpre]

Progress of the PR

• [x] Enable numpydoc and nitpicky,
• [x] docstring updated (if appropriate),
• [x] update user guide (if appropriate),
• [n/a] added tests,
• [x] add a changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• [x] Check formatting of the changelog entry (and eventual user guide changes) in the docs/readthedocs.org:holospy build of this PR (link in github checks)
• [x] ready for review.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 86.95652% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 87.23%. Comparing base (8541538) to head (790e801).

Files	Patch %	Lines
holospy/tools.py	70.00%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #30 +/- ## ======================================= Coverage 87.23% 87.23% ======================================= Files 7 7 Lines 329 329 Branches 73 73 ======================================= Hits 287 287 Misses 25 25 Partials 17 17 ```

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