docs(standard): Document how the r_0 calculation differs from the paper

[Maddiaa0]

Overview

Elaborate on the reasoning for why the implementation differs, issue created off the back of this recent comment from lasse.

                // @note that our r_0 looks different from the paper.
                // This related to the public input delta that we mentioned earlier.
                // So we are replacing PI with (z̄_ω - ∆PI) * L_n * α^2.
                // @follow-up Elaborate on this replacement
                // @note that our r_0 differs on the power of alpha from the paper. The alpha is a challenge
                // so having a different challenge is fine, as long as both verifier and prover use the same.

[LHerskind]

This section should be altered when the verifier is unrolled. Don't work on before that is done.

[LHerskind]

Also got a comment with

let r0neg := sub(p, mload(R_ZERO_EVAL_LOC)) // Change owing to the simplified Plonk @follow-up