Refactor: Convert README.rst to README.md

[JTaeuber]

Motivation

Relates to #10.

Changes

• Changed the README.rst file to a markdown file and changed a few descriptions. I left the pip install pykube-ng since we don`t have a package to install yet.
• Changed a few values in the pyproject.toml

TODO

• I've assigned myself to this PR

[JTaeuber]

There are still references to pykube-ng in the python code. This should be taken care of next.

[Fovty]

In order to keep track, here are the remaining references, right?

• README.md
• docs/index.rst
• docs/users.rst
• docs/write-an-operator.rst
• pykube/config.py
• pykube/http.py
• pykube/test_config.py
• pykube/test_http.py

[Fovty]

LGTM

[JTaeuber]

In order to keep track, here are the remaining references, right?

• README.md
• docs/index.rst
• docs/users.rst
• docs/write-an-operator.rst
• pykube/config.py
• pykube/http.py
• pykube/test_config.py
• pykube/test_http.py

Pretty much. Just keep in mind that it's docs/howtos/write-an-operator.rst to avoid confusion.