Add example to GoInterface

examples/src/go_interface.cpp

@@ -0,0 +1,21 @@
+#include <utempl/go_interface.hpp>
+#include <fmt/core.h>
+
+struct SomeInterfaceImpl {
+  int a;
+  int b;
+};
+using SomeInterface = utempl::GoInterface<SomeInterfaceImpl>;
+struct SomeStruct {
+  short a;
+  short b;
+};
+
+inline auto Func(SomeInterface arg) {
+  fmt::print("{} {}\n", arg.a, arg.b);
+};
+
+
+auto main() -> int {
+  Func(SomeStruct{42, 300});
+};