add cgo sample

cgo/helloc.go

@@ -0,0 +1,23 @@
+package main
+
+/*
+#include <stdio.h>
+#include <stdlib.h>
+
+void myprint(char* s) {
+	printf("%s", s);
+}
+*/
+import "C"
+
+import "unsafe"
+
+func Example() {
+	cs := C.CString("Hello from stdio\n")
+	C.myprint(cs)
+	C.free(unsafe.Pointer(cs))
+}
+
+func main() {
+	Example()
+}