Add onchain to the Hacktoberfest Swag List

[vimode]

A good first issue for people celebrating Hacktoberfest!

onchain is a month long Hacktoberfest event that rewards contributors through a prize pool of 500$OP for contributing to crypto, web3 and ethereum based open source projects . 🎉
Code, no-code, tutorials, documentations, etc. All contributions are welcome! ✨

Please add them to the 2024 list following the formatting in the CONTRIBUTING.md file.

You will need to locate the type of swag being offered, their requirements, and a link to their signup form (or some info on how they are tracking contributors).

Be sure to register for Hacktoberest first by clicking here.

[Brijeshthummar02]

i can do this, assign me.

[vimode]

Included in #935