docs: fix code snippet

[florian-lefebvre]

Describe your changes

There was a syntax highlighting issue in the readme.

Checklist

• [x] I have performed a self-review of my code
• [ ] I have added thorough tests
• [x] I have updated the docs

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (c23cd27) 100.00% compared to head (5a8a6ce) 100.00%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## beta #150 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 4 4 Lines 820 820 Branches 148 148 ========================================= Hits 820 820 ``` Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Yassine+Doghri). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Yassine+Doghri)

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[yassinedoghri]

Thank you for the fix @florian-lefebvre!