ssh: document that ParseRawPrivateKey supports Ed25519 keys

From CL 173457 and CL 235358.

Change-Id: Ia46ab9c7e2c57472df3126ddc7050f0068fcaab9
GitHub-Last-Rev: c38e379
GitHub-Pull-Request: #146
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/241282
Auto-Submit: Han-Wen Nienhuys <hanwen@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Han-Wen Nienhuys <hanwen@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Han-Wen Nienhuys <hanwen@google.com>

ssh/keys.go

@@ -1087,9 +1087,9 @@ func (*PassphraseMissingError) Error() string {
 	return "ssh: this private key is passphrase protected"
 }
 
-// ParseRawPrivateKey returns a private key from a PEM encoded private key. It
-// supports RSA (PKCS#1), PKCS#8, DSA (OpenSSL), and ECDSA private keys. If the
-// private key is encrypted, it will return a PassphraseMissingError.
+// ParseRawPrivateKey returns a private key from a PEM encoded private key. It supports
+// RSA, DSA, ECDSA, and Ed25519 private keys in PKCS#1, PKCS#8, OpenSSL, and OpenSSH
+// formats. If the private key is encrypted, it will return a PassphraseMissingError.
 func ParseRawPrivateKey(pemBytes []byte) (interface{}, error) {
 	block, _ := pem.Decode(pemBytes)
 	if block == nil {