chore: add contributors to README.md

[smeijer]

To quote the all-contributors page:

The basic idea is this:

Use the project README to recognize the contributions of members of the project community.

People are giving themselves and their free time to contribute to open source projects in so many ways, so we believe everyone should be praised for their contributions (code or not).

As a reminder, contributors can be added in two ways:

command line

npx all-contributors-cli add <username> <contributions>

bot

@all-contributors please add <username> for <contributions>

Contributions are comma-separated, and the types can be found here:

https://allcontributors.org/docs/en/emoji-key

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resolves: #6