README: update a few package names

Author: FiloSottile

README.md

@@ -7,8 +7,10 @@ import "filippo.io/edwards25519"
 This library implements the edwards25519 elliptic curve, exposing the necessary APIs to build a wide array of higher-level primitives.
 Read the docs at [pkg.go.dev/filippo.io/edwards25519](https://pkg.go.dev/filippo.io/edwards25519).
 
-The code is originally derived from Adam Langley's internal implementation in the Go standard library, and includes George Tankersley's [performance improvements](https://golang.org/cl/71950). It was then further developed by Henry de Valence for use in ristretto255, and was finally [merged back into the Go standard library](https://golang.org/cl/276272) as of Go 1.17. It now tracks the upstream codebase and extends it with additional functionality.
+The package tracks the upstream standard library package `crypto/internal/fips140/edwards25519` and extends it with additional functionality.
 
-Most users don't need this package, and should instead use `crypto/ed25519` for signatures, `golang.org/x/crypto/curve25519` for Diffie-Hellman, or `github.com/gtank/ristretto255` for prime order group logic. However, for anyone currently using a fork of `crypto/internal/edwards25519`/`crypto/ed25519/internal/edwards25519` or `github.com/agl/edwards25519`, this package should be a safer, faster, and more powerful alternative.
+The code is originally derived from Adam Langley's internal implementation in the Go standard library, and includes George Tankersley's [performance improvements](https://golang.org/cl/71950). It was then further developed by Henry de Valence for use in ristretto255, and was finally [merged back into the Go standard library](https://golang.org/cl/276272) as of Go 1.17.
+
+Most users don't need this package, and should instead use `crypto/ed25519` for signatures, `crypto/ecdh` for Diffie-Hellman, or `github.com/gtank/ristretto255` for prime order group logic. However, for anyone currently using a fork of the internal `edwards25519` package or of `github.com/agl/edwards25519`, this package should be a safer, faster, and more powerful alternative.
 
 Since this package is meant to curb proliferation of edwards25519 implementations in the Go ecosystem, it welcomes requests for new APIs or reviewable performance improvements.