Update package manager instructions in README.md

[khalil7044]

Added a short note at the end of README.md for Ubuntu and Debian users who may need to install nodejs and npm before using yarn install

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[wackerow]

Thanks @khalil7044... This project uses pnpm as it's primary package manager at this point and using yarn could lead to package inconsistencies, and add undesired changes if users take this approach before submitting PRs. Ideally we make this clear instead of adding more instructions about how to use yarn.

(Would also try to find a better spot for such an update than below the "Back to top" link 😉)

[wackerow]

I've gone ahead and adjusted this to remove yarn comments, replacing with corepack enable and pnpm install, and moved this up in the section that handles these steps. Thanks @khalil7044!

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[wackerow]

@all-contributors please add @khalil7044 for infra