Move information from README to documentation

[padix-key]

This PR collects information previously residing in the README and puts it into the documentation, primarily into the Contributor guide.

[padix-key]

@naefl I actually removed most sections from the README.md entirely, as they now reside in the docs which is linked in README.md. In my opinion this gives the user just enough information to catch the attention and encourage them to read the documentation for further details. Do you agree?

[naefl]

Hmmm, I personally wouldn't do this. I think 1) many, if not most, people prefer not having to interact with the python api and just take the files from the buckets 2) the current python install still doesn't work well on macOS due to openstructure 3) every extra link people have to click to get started is extra friction.

I think we should leave the current getting started, my understanding is this new getting started won't even work outside of docker, so until that is resolved I don't think we should advertise the python api much, and even then we should have a minimal "don't-have-to-click-extra-links" getting started on the README.md.

Agree with moving the the dev instructions though.

[padix-key]

I actually agree. My proposal is more about moving more detailed section, such as the workflow description, into the docs. The Getting started section now mentions the Google Bucket, but the Python installation instructions still needs improvement. This will be covered in an upcoming PR this week, where plinder is released on PyPI.

[naefl]

Sounds good - right now the Getting Started in the README.md AFAICT removes instructions of how to use the data from the bucket and leaves the python installation instructions - I assume you'll invert that later (i.e. do the opposite: remove python, add back the instructions how to use the data from the bucket)

[padix-key]

I readded the dataset download instructions