pythongh-124832: Add a note to indicate that datetime.now may retur…

…n the same instant (python#124834)

* Update datetime.rst

* Update datetime.rst

replace warning with note

* Update Doc/library/datetime.rst

Co-authored-by: Victor Stinner <vstinner@python.org>

* Update Doc/library/datetime.rst

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

---------

Co-authored-by: Victor Stinner <vstinner@python.org>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

Doc/library/datetime.rst

@@ -948,6 +948,10 @@ Other constructors, all class methods:
 
    This function is preferred over :meth:`today` and :meth:`utcnow`.
 
+   .. note::
+
+      Subsequent calls to :meth:`!datetime.now` may return the same
+      instant depending on the precision of the underlying clock.
 
 .. classmethod:: datetime.utcnow()