Sorbet type signatures

[olivier-thatch]

Some weeks ago I submitted Sorbet type signatures for the money gem to the rbi-central repo (PR).

Would you consider adding type signatures directly in the gem?

To clarify: this would mean adding RBI files with the signatures in an rbi/ directory distributed as part of the gem (cf. Sorbet docs), not adding a dependency on sorbet-runtime or adding the signatures inline with their methods. Non-Sorbet users would not be affected.

If you're open to this, I will submit a PR.