Adding plotting specific documentation

Comment originally from @MeyerBender, thanks for the feedback!

documentation: in general, I think it would be good to have one or two notebooks that exclusively focus on visualization. Right now, it is very hard to find this in the spatialdata docs. Maybe something similar to this, which shows off the most important plotting functions in spatialproteomics.

Currently we have plotting notebooks but hidden under the "Technology-specific" section in the docs. And we have another notebook in a separate repo (=not really discoverable).

Improving the docs with a visualization-specific notebook that is easily discoverable would be valuable.

まず、ドキュメントの「Technology-specific」セクションにある plotting notebook と、既存の spatialdata-workshops/notebooks/nb2_static_plotting.ipynb を確認します。主要な plotting 関数と、ドキュメント内で notebook がどのようにリンクされているかを特定します。visualization に焦点を当てた notebook が spatialdata-plot のドキュメントで見つけやすく、重要な plotting 関数を網羅していれば完了です。