Update Contribution guidelines?

[asvishnyakov]

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I followed contribution guidelines to install dependencies, build, test & create PR, but had a few issues:

1. Pre-commit checks fails with the following error:

2. poetry build produces wheel without frontend and copilot folders inside, but with the following log:

Ubuntu 24.04 Python 3.12.3 Poetry 2.0.1 pnpm 9.13.2 (selected automatically by poetry and/or corepack)