add export explanation

Author: xuantengh

Include/internal/pycore_optimizer.h

@@ -110,6 +110,8 @@ void _Py_ExecutorInit(_PyExecutorObject *, const _PyBloomFilter *);
 void _Py_ExecutorDetach(_PyExecutorObject *);
 void _Py_BloomFilter_Init(_PyBloomFilter *);
 void _Py_BloomFilter_Add(_PyBloomFilter *bloom, void *obj);
+
+// Export for '_testinternalcapi' shared extension.
 PyAPI_FUNC(void) _Py_Executor_DependsOn(_PyExecutorObject *executor, void *obj);
 
 // For testing
@@ -273,6 +275,7 @@ extern int _Py_uop_frame_pop(_Py_UOpsContext *ctx);
 
 PyAPI_FUNC(PyObject *) _Py_uop_symbols_test(PyObject *self, PyObject *ignored);
 
+// Export for '_testinternalcapi' shared extension.
 PyAPI_FUNC(int) _PyOptimizer_Optimize(struct _PyInterpreterFrame *frame, _Py_CODEUNIT *start, _PyStackRef *stack_pointer, _PyExecutorObject **exec_ptr, int chain_depth);
 
 static inline int is_terminator(const _PyUOpInstruction *uop)