[FEATURE REQUEST] Improved documentation for `cairo`

[ElectrifyPro]

Currently, the documentation for the cairo crate is unfortunately quite empty compared to the other core crates in this repository, and there isn't any information or clear entry point (apart from external sources) to help users get started with the crate. It would be extremely convenient to have a short guide to getting started, and complete documentation, even if it's pulled directly from the C API reference. I'd personally be glad to assist in any way here.

Some very useful cairo structs that have sparse documentation:

Context ImageSurface TextExtents