Add detailed documentation

[Hello-world150]

I want to use this crate to implement an operating system, but I'm confused about the example implementation of the log mentioned in framebuffer.rs.
Could you please add detailed documentation so that it can be easy to use.
Thank you.

[Freax13]

Please read https://github.com/rust-osdev/bootloader?tab=readme-ov-file#usage. I don't think framebuffer.rs is meant to be used as an example for a logging implementation, it's primarily meant to be the logging implementation used by the bootloader. If you can use it for inspiration that's great, but its primary purpose is not education.