Terminology nit: package ID rather than package address

[sblackshear]

In the readme for the gen.toml:

# an on-chain package:
FooPackage = { address = "0x12345" }

Might be clearer to use id = instead of address. I would just send a PR to update the README, but i'm guessing the toml parser (and maybe other code) uses address as well.