Docs: Rollup-boost guide

[odyslam]

I have seen #383 but it's not obvious on how to setup Rollup-Boost and most specifically that it should be pointed to the Engine RPC of the Reth part of rbuilder, which is dfferent from the json_rpc config value in the rbuilder toml.

As rbuilder is essentially configured in two places (cli -> reth, toml -> rbuilder) it would be great if there was a simple guide on how to setup everything and what should go into which configuration path.

[avalonche]

op-rbuilder is separate from rbuilder and does not have the same set of configs. The whole setup up will be in the rollup-boost docs, this is for op-rbuilder specific config.

[avalonche]

Please see flashbots/rollup-boost#66 and local devnet params for the whole e2e flow