bpo-46906: Mention native endian in PyFloat_Pack8() doc (GH-31866)

Author: vstinner

Doc/c-api/float.rst

@@ -109,7 +109,9 @@ Pack functions
 The pack routines write 2, 4 or 8 bytes, starting at *p*. *le* is an
 :c:type:`int` argument, non-zero if you want the bytes string in little-endian
 format (exponent last, at ``p+1``, ``p+3``, or ``p+6`` ``p+7``), zero if you
-want big-endian format (exponent first, at *p*).
+want big-endian format (exponent first, at *p*). The :c:data:`PY_BIG_ENDIAN`
+constant can be used to use the native endian: it is equal to ``1`` on big
+endian processor, or ``0`` on little endian processor.
 
 Return value: ``0`` if all is OK, ``-1`` if error (and an exception is set,
 most likely :exc:`OverflowError`).
@@ -138,7 +140,9 @@ Unpack functions
 The unpack routines read 2, 4 or 8 bytes, starting at *p*.  *le* is an
 :c:type:`int` argument, non-zero if the bytes string is in little-endian format
 (exponent last, at ``p+1``, ``p+3`` or ``p+6`` and ``p+7``), zero if big-endian
-(exponent first, at *p*).
+(exponent first, at *p*). The :c:data:`PY_BIG_ENDIAN` constant can be used to
+use the native endian: it is equal to ``1`` on big endian processor, or ``0``
+on little endian processor.
 
 Return value: The unpacked double.  On error, this is ``-1.0`` and
 :c:func:`PyErr_Occurred` is true (and an exception is set, most likely