remove empty creds restriction (#10)

* removed empty checks on qbit and deluge credentials

* updated configuration readme

code/Common/Configuration/QBitConfig.cs

@@ -25,15 +25,5 @@ public sealed class QBitConfig : IConfig
         {
             throw new ArgumentNullException(nameof(Url));
         }
-
-        if (string.IsNullOrEmpty(Username))
-        {
-            throw new ArgumentNullException(nameof(Username));
-        }
-
-        if (string.IsNullOrEmpty(Password))
-        {
-            throw new ArgumentNullException(nameof(Password));
-        }
     }
 }