Include which command failed to build on exception

src/Discord.Net.Commands/Command.cs

@@ -30,6 +30,8 @@ namespace Discord.Commands
         public IReadOnlyList<PreconditionAttribute> Preconditions { get; }
 
         internal Command(MethodInfo source, Module module, object instance, CommandAttribute attribute, string groupPrefix)
+        {
+            try
             {
                 Source = source;
                 Module = module;
@@ -65,6 +67,11 @@ namespace Discord.Commands
                 Preconditions = BuildPreconditions(source);
                 _action = BuildAction(source);
             }
+            catch (Exception ex)
+            {
+                throw new Exception($"Failed to build command {source.DeclaringType.FullName}.{source.Name}", ex);
+            }
+        }
 
         public async Task<PreconditionResult> CheckPreconditions(IUserMessage context)
         {