Add quick start command

[dmarzzz]

No description provided.

[zeroXbrock]

We have a zero-config command contender run that has (at the moment) a single default scenario to run.
Try this:

Run anvil with timed blocks:

anvil -b 1

Then in another shell, run this:

cargo run -- run fill-block http://localhost:8545

if you want to run this on a live network, you just need to add a private key:

cargo run -- run fill-block $RPC_URL -p $YOUR_PRV_KEY

The fill-block scenario will just fill a block to its gas limit.
There's a secret environment variable that allows you to fill less than 100% of the block if desired:

export C_FILL_PERCENT=50
cargo run -- run fill-block $RPC_URL -p $YOUR_PRV_KEY

This just needs to be documented.

[zeroXbrock]

added examples in readme to illustrate the zero-config option (currently only fill-block but may expand later) in this pr: #78