Improving docs for the getting started section

[cwkang1998]

In the getting started section -> Proving circuits with ZK, the contents can be a bit clearer. I believe (and I might be wrong, new into circom) that there's a missing beacon step for the phase 2 section of the doc, where its lacking a snarkjs beacon to end the phase, which is actually documented here https://github.com/iden3/snarkjs/blob/master/README.md.

Would love to see that added to the docs, and also with a bit more clarity to only use the final zkey for exporting verifier.sol, since only then will the verifier work as expected when verifying the inputs (clearly I got bitten by this xD).

Would be happy to add to the docs on this as well!

[rkdud007]

LGTM, we need to add to docs for prevent later confusion!