docs to generate GnarkPlonk proofs

[jotabulacios]

How to test

After generating the proof, you will have to have three different files:

• proof file
• verification key file
• public input file

Then, you can send the proof to the AlignedLayer network by running the following command
from batcher/client folder inside the AlignedLayer repository directory:

cargo run --release -- \
--proving_system GnarkPlonkBn254 \
--proof <proof_path> \
--public_input <public_input_path> \
--vk <verification_key_path> \

[jotabulacios]

I'm not sure if this guide is the best for generating a proof. Maybe we could add a HackMD
https://hackmd.io/@xr7wfZ30Q3eKDrtinAJaOQ/B1cp2nV4A

[MauroToscano]

change the Docs file to docs/gnark_example.md, then link it in the readme

[MauroToscano]

• Gnark version should be pinned to the one we use in Aligned, not latest
• We already have a section for sending Gnark Proofs, we can add the new text to that one. The important part is to mention you have to add code to your circuit to export the data Aligned needs. We can link the guide on how to do so. It should be one paragraph more, or a couple of lines

[Oppen]

Converted to draft due to not being a priority for mainnet