Initial draft architecture for FAQ/Troubleshooting.

[bobbyxng]

Changes proposed in this Pull Request

• Following @nworbmot's suggestion, proposing a draft skeleton for a potential FAQ/troubleshooting guidelines for common model issues/challenges
• Draft: Open for discussion and FAQ proposals
• https://pypsa-eur--1939.org.readthedocs.build/en/1939/

Checklist

• [X] I tested my contribution locally and it works as intended.
• [ ] Code and workflow changes are sufficiently documented.
• [ ] Changed dependencies are added to pixi.toml (using pixi add <dependency-name>).
• [ ] Changes in configuration options are added in config/config.default.yaml.
• [ ] Changes in configuration options are documented in doc/configtables/*.csv.
• [ ] For new data sources or versions, these instructions <https://pypsa-eur.readthedocs.io/en/latest/data_sources.html>_ have been followed.
• [ ] A release note doc/release_notes.rst is added.

[fneum]

Sure, great idea! But would keep it simple without the expansion: better Ctrl+F experience and less code.