Update "crate level API" docs

This line is a bit stale, since it was written we have added multiple
crate level APIs. Use the same wording as in the `decode` module docs.

src/primitives/encode.rs

@@ -7,7 +7,7 @@
 //! prepending HRP strings etc.
 //!
 //! In general, directly using these adaptors is not very ergonomic, and users are recommended to
-//! instead use the higher-level functions at the root of this crate.
+//! instead use the higher crate level API.
 //!
 //! # Examples
 //!