Add better help message on non-trivial usage of some types

[ifropc]

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Some of types are not trivial to pass (and we don't have any documentation or anything on how to do so) For example, with this signature (coming from account example)

pub fn __constructor(env: Env, signers: Vec<BytesN<32>>) {

How do I actually pass Vec<BytesN<32>> into the cli?