Docs: Clarify that random.seed() discards the sign of an integer input

If *a* is an integer, the sign of *a* is discarded in the C source code. Clarify this behavior to prevent foot guns, where a common use case might naively assume that flipping the sign will produce different sequences (e.g. for a train/test split of a synthetic data generator in machine learning).

Author: karpathy

Doc/library/random.rst

@@ -78,7 +78,9 @@ Bookkeeping functions
    instead of the system time (see the :func:`os.urandom` function for details
    on availability).
 
-   If *a* is an int, it is used directly.
+   If *a* is an int, it is used directly. Note that negative integer seeds are 
+   treated as equivalent to their absolute value, so for example ``seed(-5)`` and
+   ``seed(5)`` will produce identical sequences.
 
    With version 2 (the default), a :class:`str`, :class:`bytes`, or :class:`bytearray`
    object gets converted to an :class:`int` and all of its bits are used.