book: Start building the rbuilder book

Dear rbuilder Core Team,

I'm a backend developer and technical writer currently exploring rbuilder and also a code contributor to [reth](https://github.com/paradigmxyz/reth). I've been following rbuilder's progress for several months and have been impressed with its rapid growth.

I am eager to make a significant contribution to rbuilder, but have found that setting up the environment has been quite time-consuming. I'm thrilled to see that rbuilder has reached its first major release, version 1.0.0, indicating a more stable and user-friendly future. However, during recent testing, I discovered that the documentation could be improved. I submitted issue [#559](https://github.com/flashbots/rbuilder/issues/558) and an associated [PR](https://github.com/flashbots/rbuilder/pull/566) to address this, which unfortunately was **rejected**, possibly due to its perceived triviality.

With rbuilder now at version 1.0.0, I believe it would greatly benefit from having its own comprehensive documentation, similar to [reth's](https://reth.rs/) and [Lighthouse's](https://lighthouse-book.sigmaprime.io/#lighthouse-book). I've noticed that rbuilder already has the domain [rbuilder.rs](http://rbuilder.rs/) reserved, so the next logical step would be to develop this resource. I am confident in my ability to contribute to this effort, it will also give me opportunity to deepen my rbuilder understanding for any future code contributions.

To ensure alignment with your priorities and to avoid duplication of effort, I kindly request the **approval and assignment** before initiating any work.

I look forward to your response and the opportunity to contribute further to rbuilder's success.