Summary:
This patch creates a new binary, `./bin/sc2`, which will be the home for
a rewrite of the CLI intended to implement an instance system. See:
<https://discourse.sourcecred.io/t/sourcecred-instance-system/244>
Paired with @decentralion.
Test Plan:
Run `yarn backend && node ./bin/sc2.js`, which should nicely fail with a
“not yet implemented” message.
wchargin-branch: cli2-skeleton