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