DOC: Update versions in readme/docs + small improvements

[theroggy]

Update versions in readme/docs + small improvements:

• remove max version of python and GDAL: triggered by Support GDAL 3.12 #594, I think it is easier not to mention to highest version of python/GDAL being supported in the readme/docs, but only the minimal version. It is impractical to keep them up-to-date and in general the most recent version is supported in a timely manner. Shapely and geopandas also don't mention these in their docs...
• clarify that the GDAL version in the wheels is not always the most recent version + how you can check the version
• fix so special attributes like __version__, __gdal_version__,... are now listed in API reference + can be linked to
• change pyogrio functions being mentioned in install.md and introduction.md to cross-links to the API docs of the functions
• the environments.yml file in docs pinned very old versions -> update to recent versions

[jorisvandenbossche]

Thanks, looks good!

[jorisvandenbossche]

• remove max version of python and GDAL: triggered by Support GDAL 3.12 #594, I think it is easier not to mention to highest version of python/GDAL being supported in the readme/docs, but only the minimal version. It is impractical to keep them up-to-date and in general the most recent version is supported in a timely manner. Shapely and geopandas also don't mention these in their docs...

+1

• the environments.yml file in docs pinned very old versions -> update to recent versions

The reason this was pinned in the past was to avoid slow doc builds, so we should be careful with removing pins from some of the deps. But I checked the readthedocs build logs, and it is not actually slower at all (nowadays, with mamba). So looks good!