Fix a TODO

enzevalos_iphone/MailAccount.swift

@@ -12,7 +12,7 @@ class MailAccount {
     
     let emailAddress: String
     let password: String
-    //TODO: describe what username is
+    // Username used for imap/smtp protocol. This can be different than emailAddress. Currently we do not support different usernames for imap and smtp
     let username: String?
     let imapServer: String
     let imapPort: Int