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> \