Update docs and contributing files to facilitate access to OEO for new users

[chrwm]

Description of the issue

So far only instructions for implementations--> wiki/how to implement

• Revise CONTRIBUTING and explain requirements (Academy course, meetings, interaction with issues) and refer to wiki, but details elsewhere
• Read and sort wiki, Academy course and contributing again
  • wiki
  • academy course
  • contributing
• Readme as an introduction, work out the collaboration section and refer to the rest https://contributing.md/how-to-build-contributing-md/

Workflow checklist

• I am aware of the workflow for this repository

[madbkr]

So far only instructions for implementations--> wiki/how to implement

I am not sure what the OP wanted here. The wiki has a whole list of different tutorials, none of them named "how to implement". There is however a "how to contribute" which links to CONTRIBUTING.md.
Maybe the issue was already resolved when the wiki got reworked. In any case I don't see what else I could do here.

Revise CONTRIBUTING and explain requirements (Academy course, meetings, interaction with issues) and refer to wiki, but details elsewhere

PR #1937 will tackle those changes, adding to the prerequisites and adding some links.

Read and sort wiki, Academy course and contributing again

Wiki was already done, CONTRIBUTING was is in PR #1937.
Academy still needs to be done.

Readme as an introduction, work out the collaboration section and refer to the rest https://contributing.md/how-to-build-contributing-md/

Readme collaboration section was expanded a bit but I didn't feel like it was missing so much. I provided more links for further reading, helping newcommers to identify the best articles to start with.
I don't know why the link the the contributing-best-practices website was linked here, but I used some of the suggestions when reworking the file.

[madbkr]

This PR OpenEnergyPlatform/academy#247 is a rework for the academy course. I made changes that I believe would have aided me as a newcomer by adding to descriptions and providing more helpful links.