docs: updated contributor guide

[musslick]

Description

This PR updates the contributor guide to the current version of autora 4.0.0 (see detailed list of fixed below).

• resolves #625
• resolves #557

Type of change

• docs: Documentation only changes

Features (Optional)

• removal of the autora-workflow package from the description of core packeges.
• updated examples of theorist and experimentalist implementations, primarily to be based on pandas dataframes
• added requirement for contributor repo to be public for inclusion in autora package

Questions (Optional)

• In the modules/index.md the lists inside the Success and Hint boxes aren't rendering properly. They are just listed without a line brak. I tried changing the "-" to "*" but not sure if that fixed it?

[hollandjg]

• In the modules/index.md the lists inside the Success and Hint boxes aren't rendering properly. They are just listed without a line brak. I tried changing the "-" to "*" but not sure if that fixed it?

They're just missing a couple of newlines. I've pushed an extra commit which makes the block look like:

!!! success

    In order for your package to be included in the parent package, it must meet the following criteria:

    * have basic documentation in ``docs/index.md``
    * have a basic python notebook exposing how to use the module in ``docs/Basic Usage.ipynb``
    * have basic tests in ``tests/``
    * be published via PyPI or Conda
    * be compatible with the current version of the parent package
    * follow standard python coding guidelines including PEP8
    * the repository in which your package is hosted must be public

The following demonstrates how ...

... which renders like:

[musslick]

Hi Sebastian, this looks great! The information is really clear and concise, and covers everything. The documentation looks really awesome. I've a couple of very minor changes to suggest, some of which are in a separate PR. #629

Thanks a lot John for all the fixes! I approved the request with all the fixes you implemented.