Fix hilarious typo.
With continuing thanks to good eyes:
// - schema -- interfaces for working with IPLD Schemas and Nodes
// which use Schema types and constraints
//
-// Note that since packages in this interface are the core of the library,
+// Note that since interfaces in this package are the core of the library,
// choices made here maximize correctness and performance -- these choices
// are *not* always the choices that would maximize ergonomics.
// (Ergonomics can come on top; performance generally can't.)
