update doc

Include/internal/pycore_symtable.h

@@ -161,6 +161,11 @@ extern PyObject* _Py_Mangle(PyObject *p, PyObject *name);
 #define SCOPE_OFFSET    11          /* 1 + highest bit for a DEF_* flag */
 #define SCOPE_MASK      0b111       /* 3 bits for storing the scope */
 
+// Scopes for a symbol.
+//
+// GLOBAL_EXPLICIT and GLOBAL_IMPLICIT are used internally by the symbol
+// table. For symbols with such scopes, the ``symtable.Symbol.is_global``
+// method returns True.
 #define LOCAL 1
 #define GLOBAL_EXPLICIT 2
 #define GLOBAL_IMPLICIT 3