Better error message

compiler/NubLang/Syntax/Parser.cs

@@ -79,8 +79,8 @@ public sealed class Parser
                     Symbol.Func => ParseFunc(startIndex, exported, null),
                     Symbol.Struct => ParseStruct(startIndex, exported),
                     _ => throw new ParseException(Diagnostic
-                        .Error($"Expected 'func' or 'struct' but found '{keyword.Symbol}'")
-                        .WithHelp("Valid definition keywords are 'func' and 'struct'")
+                        .Error($"Expected 'func', 'struct', 'import' or 'module' but found '{keyword.Symbol}'")
+                        .WithHelp("Valid top level statements are 'func', 'struct', 'import' and 'module'")
                         .At(keyword)
                         .Build())
                 };