test: move cgo demo into _testgo, and make links

cl/_testgo/cgopython/cgopython.go

@@ -0,0 +1,13 @@
+package main
+
+/*
+#cgo pkg-config: python3-embed
+#include <Python.h>
+*/
+import "C"
+
+func main() {
+	C.Py_Initialize()
+	defer C.Py_Finalize()
+	C.PyRun_SimpleString(C.CString("print('Hello, Python!')"))
+}