Check in chain spec for mainnet when we launch

[blakebyrnes]

Note: Non-Determinism in Wasm & chain specs: Because Rust -> Wasm optimized builds aren't reproducible, each person will get a slightly different Wasm blob which will break consensus if each participant generates the file themselves. For the curious, learn more about this issue in this blog post.

It is conventional to include the chain specification files for your node within the source code itself so that anyone can build your node in the same way, whereby it becomes easy to check for non-determinism by comparing a genesis blob with another. Polkadot, Kusama, Rococo, and more network chain spec files are found in the source here along with a .gitignore file to ensure that you don't accidentally change these !/*.json files as you build further on your node's software and do runtime upgrades.

• https://substrate.stackexchange.com/a/2348/4545
• https://github.com/paritytech/polkadot/tree/master/node/service/chain-specs