Changes proposed in this Pull Request

Add an example notebook demonstrating uniform-price market clearing with supply and demand bids. It shows supply/demand curves, solves a single‑zone welfare‑maximization, then splits bids into two zones to show zonal price separation and the effect of adding an interconnector.

Other changes:

• loads.md: better explain when and how to use generators as substitute for loads and link the example notebook
• mkdocs.yml: add the example

Checklist

• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in docs.
• Unit tests for new features were added (if applicable).
• A note for the release notes docs/release-notes.md of the upcoming release is included.
• I consent to the release of this PR's code under the MIT license.