Optimize contribution guidelines

[mfranzke]

Currently we're having two sections for contributions within our README file – we should most likely merge this to one, and even also extract relevant information to the separate CONTRIBUTING.md file.

That file would additionally need some more rework, as we're currently mentioning the husky dependency, but especially for somebody new to the project don't mention how they should do this, as in general this dependency would get installed by the general npm install:
https://github.com/db-ui/core/blob/main/CONTRIBUTING.md?plain=1#L9

Besides that we should mention some prerequisites like e.g. nvm that would ensure the expected node version to be installed.

[ErebusXAbyss]

I would like to work on this issue