ed25519: update godoc for consts in crypto/ed25519

This is a follow-up to Change-Id: I860ed963a0660753d01c89014c21360b239a38ac
(commit 20e1d8d), which dropped compatibility
with go1.12, and made this package an alias / wrapper for crypto/ed25519 in
stdlib.

This patch updates their godoc to include a docs-link to the equivalent
consts in stdlib.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Author: thaJeztah

ed25519/ed25519.go

@@ -23,12 +23,20 @@ import (
 
 const (
 	// PublicKeySize is the size, in bytes, of public keys as used in this package.
+	//
+	// This const is an alias for [crypto/ed25519.PublicKeySize].
 	PublicKeySize = 32
 	// PrivateKeySize is the size, in bytes, of private keys as used in this package.
+	//
+	// This const is an alias for [crypto/ed25519.PrivateKeySize].
 	PrivateKeySize = 64
 	// SignatureSize is the size, in bytes, of signatures generated and verified by this package.
+	//
+	// This const is an alias for [crypto/ed25519.SignatureSize].
 	SignatureSize = 64
 	// SeedSize is the size, in bytes, of private key seeds. These are the private key representations used by RFC 8032.
+	//
+	// This const is an alias for [crypto/ed25519.SeedSize].
 	SeedSize = 32
 )