add semaphore and world id use case

[kichong]

Description

this adds a section to the zero-knowledge proofs page called proof of humanity that mentions the semaphore protocol used by world id.

Preview link

https://deploy-preview-15673--ethereumorg.netlify.app/en/zero-knowledge-proofs#proof-of-humanity

Related Issue

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[wackerow]

Thanks a lot @kichong! Looking forward to more updates on this page

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[wackerow]

@all-contributors please add @kichong for content

[allcontributors]

@wackerow

I've put up a pull request to add @kichong! 🎉