Update Doc/extending/embedding.rst

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>

Author: neonene

Doc/extending/embedding.rst

@@ -252,8 +252,14 @@ Python extension.  For example::
    };
 
    static PyModuleDef_Slot emb_module_slots[] = {
+   #ifdef Py_mod_multiple_interpreters
+       // signal that this module can be imported in isolated subinterpreters
        {Py_mod_multiple_interpreters, Py_MOD_PER_INTERPRETER_GIL_SUPPORTED},
+   #endif
+   #ifdef Py_mod_gil
+       // signal that this module supports running without an active GIL
        {Py_mod_gil, Py_MOD_GIL_NOT_USED},
+   #endif
        {0, NULL}
    };