chore: add recommendations to documentation of hash functions.

README.md

@@ -9,11 +9,11 @@ Here is an example of usage:
 ```go
 func Example() {
 	pass := "my_pass"
-	hash := "my_pass"
+	hash := "$1$81ed91e1131a3a5a50d8a68e8ef85fa0"
 
 	pwd := passwd.New(
-		&unix.MD5{}, // first is preferred type.
-		&plainPasswd{},
+		argon2.Argon2id, // first is preferred type.
+		&unix.MD5{},
 	)
 
 	_, err := pwd.Passwd(pass, hash)
@@ -32,7 +32,7 @@ func Example() {
 	}
 
 	// Output:
-	//  new hash: $1$81ed91e1131a3a5a50d8a68e8ef85fa0
+	//  new hash: $argon2id$...
 }
 ```
 https://github.com/sour-is/go-passwd/blob/main/passwd_test.go#L33-L59

passwd_test.go

@@ -30,6 +30,9 @@ func (p *plainPasswd) ApplyPasswd(passwd *passwd.Passwd) {
 	passwd.SetFallthrough(p)
 }
 
+// Example of upgrading password hash to a greater complexity.
+//
+// Note: This example uses very unsecure hash functions to allow for predictable output. Use of argon2.Argon2id or scrypt.Scrypt2 for greater hash security is recommended.
 func Example() {
 	pass := "my_pass"
 	hash := "my_pass"

pkg/unix/unix_test.go

@@ -14,7 +14,7 @@ func TestPasswdHash(t *testing.T) {
 	type testCase struct {
 		pass, hash string
 	}
-	
+
 	tests := []testCase{
 		{"passwd", "$1$76a2173be6393254e72ffa4d6df1030a"},
 		{"passwd", "$2a$10$GkJwB.nOaaeAvRGgyl2TI.kruM8e.iIo.OozgdslegpNlC/vIFKRq"},