Doc: Improve new contributor documentation

As a **new contributor** you are for a very short time in a **unique position**: You can judge whether the [CONTRIBUTING.md](https://github.com/cleodora-forecasting/cleodora/blob/main/CONTRIBUTING.md) and [Development Documentation](https://github.com/cleodora-forecasting/cleodora/tree/main/dev_docs) is good enough!

People who have been around the project longer suffer from the _curse of knowledge_ and are no longer able to accurately judge the quality of this documentation.

* Was there any place where you got stuck, had to google or ask for help?
* Was there anything incorrect or out of date?
* Was there anything missing that once you learnt it, really helped you make progress?

**Please fix it!** If you identified a problem, but don't know how to fix it yourself, open a new issue or add a comment to the current issue.

As with any other issue, if you plan major rewrites it is best to discuss them first to avoid you going to a lot of trouble, only to have the changes rejected. You can add a comment to this issue to explain what you would like to do.

This issue will forever remain open with the 'good first issue' label. The reason is that there will always be new contributors and the documentation will always be lacking in some sense. Comments in this ticket will be deleted once they have been answered or resolved.

Start by reading CONTRIBUTING.md and the Development Documentation in dev_docs, then follow the documented setup and contribution path. Note where you get stuck, find outdated information, or need missing context, and make a focused documentation improvement. Done means the identified contributor-facing problem is corrected and the relevant guidance is clearer.

Written by the indexing model from the issue text.