Add install instruction, micro synopsis to README

[nicholasjng]

Currently non-functional, until the final PyPI names have been decided.

Emphasizes the split between the two packages, and mentions which user persona likely needs which package.

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Still missing:

• Links to contribution guides, mentions of the license, and so on.
• Badges (if we want them).

And the same discussion as before applies: What goes into the readme? Do we give an example? Do we link to the quickstart guide? Do we use special media (screen recording of the CLI, job defs, etc.)?

Happy for inputs.

[nicholasjng]

NB: Reviews can be content-based, but also include opinions on direction. I'm not trying to be lazy here, just want to coordinate the direction before committing to a specific presentation, since this is a rather important document.

[AdrianoKF]

Overall, I would put less emphasis on the installation (just mention it as a one-liner), but rather elaborate on the usage example (basically show the @job-decorated workflow as Python code and the CLI invocation used to submit the job and maybe to get its logs).

In lakeFS-spec, we also had sections "Contributing" and "License", I think it makes sense to include those as well.

I would not talk about the deployment of the server-side components at all, other than mentioning that jobs are scheduled on Kubernetes.