cli: add output message to init command and move example-overrides.json to root

[evgeniko]

• moving example-overrides.json to root makes it easier for devs to configure custom RPCs. They can simply rename the file instead of having to find and move it first.

• the added output to the init command will illustrate its usage more:

❯ ntt init Testnet
deployment.json created — this file stores your NTT deployment configuration

Tip: To use custom RPC endpoints, rename example-overrides.json to overrides.json and edit as needed.