Improve readme for AI agentic coding

[nicolasdao]

The aim of this PR is to provide a single README.md file that can be easily pasted into system prompts so AI coding agents (e.g., ChatGPT) can immediately understand how to use the crate.

To achieve this, this update compiles all the existing code examples scattered throughout the source code into one cohesive and comprehensive README.md file. This creates exhaustive documentation of the crate's API in a single, easy-to-navigate document, making it simpler for both humans and LLMs to explore and apply the crate effectively.

[s3bk]

Hello, while I don't think AI coding is a good idea, I welcome your effort to making a good entry point to the library.
I have to read the whole thing in a bit, and then I will see if changes are needed to merge it.

[nicolasdao]

Not a problem. I'm using this for myself as I had to create that document in order to smoothly let Claude AI integrate pdf into my app. I thought this doc could be useful to someone else, hence this PR. I fully appreciate your opinion and I thank you a lot for this awesome library.

Cheers,

Nic