Update Help output

Trying to use `-url` throws:

```sh
Could not parse command line parameter '-url'.
An unexpected error occurred | [GitHubLinkException] GitHubLink.GitHubLinkException: Could not parse command line parame
ter '-url'.
   at Catel.Logging.LogExtensions.ErrorAndThrowException[TException](ILog log, String messageFormat, Object[] args) in c:\CI_WS\Ws\1459\Source\Catel\src\Catel.Core\Catel.Core.NET40\Logging\Extensions\LogExtensions.cs:line 362
   at GitHubLink.ArgumentParser.ParseArguments(List`1 commandLineArguments)
   at GitHubLink.Program.Main(String[] args)
```