Fix typo on PPLM example README

[Beomi]

What does this PR do?

Fix PATH typo on PPLM example README.

Fixes # (issue)

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• Did you make sure to update the documentation with your changes? Here are the
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• Did you write any new necessary tests?

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[LysandreJik]

Great, thank you!