Improve help command text (#55)

So that's clearer how to get information about a command

Author: matt-richardson

source/CommandLine/Commands/HelpCommand.cs

@@ -5,7 +5,7 @@
 
 namespace Octopus.CommandLine.Commands
 {
-    [Command("help", "?", "h", Description = "Prints this help text.")]
+    [Command("help", "?", "h", Description = "Prints this help text. Pass the name of a command to see the arguments required for that command.")]
     public class HelpCommand : CommandBase
     {
         readonly Lazy<ICommandLocator> commands;
@@ -108,4 +108,4 @@ public void PrintJsonOutput()
                 }));
         }
     }
-}
+}