Use readKeyFile to read both seed file and public key file

It's consistent with the key reading behavior in `sign`, and we can add some
comments in both seed file and public key file.

Signed-off-by: JUN JIE NAN <nanjunjie@gmail.com>

nk/main.go

@@ -170,19 +170,11 @@ func verify(fname, keyFile, pubFile, sigFile string) {
 	var err error
 	var kp nkeys.KeyPair
 	if keyFile != "" {
-		var seed []byte
-		seed, err = os.ReadFile(keyFile)
-		if err != nil {
-			log.Fatal(err)
-		}
+		seed := readKeyFile(keyFile)
 		kp, err = nkeys.FromSeed(seed)
 	} else {
 		// Public Key
-		var public []byte
-		public, err = os.ReadFile(pubFile)
-		if err != nil {
-			log.Fatal(err)
-		}
+		public := readKeyFile(pubFile)
 		kp, err = nkeys.FromPublicKey(string(public))
 	}
 	if err != nil {