Swift: Add GOOD and BAD comments.

Author: geoffw0

swift/ql/src/queries/Security/CWE-328/WeakPasswordHashingBad.swift

@@ -1,5 +1,5 @@
 let passwordData = Data(passwordString.utf8)
-let passwordHash = Crypto.SHA512.hash(data: passwordData)
+let passwordHash = Crypto.SHA512.hash(data: passwordData) // BAD: SHA-512 is not suitable for password hashing.
 
 // ...
 

swift/ql/src/queries/Security/CWE-328/WeakPasswordHashingGood.swift

@@ -1,7 +1,7 @@
 import Argon2Swift
 
 let salt = Salt.newSalt()
-let result = try! Argon2Swift.hashPasswordString(password: passwordString, salt: salt)
+let result = try! Argon2Swift.hashPasswordString(password: passwordString, salt: salt) // GOOD: Argon2 is suitable for password hashing.
 let passwordHash = result.encodedString()
 
 // ...