add doc for buffersize argument

Author: obaltian

Misc/NEWS.d/next/Library/2025-07-28-00-18-06.gh-issue-64192.t9b0XO.rst

@@ -0,0 +1,6 @@
+Add the optional ``buffersize`` parameter to
+:meth:`multiprocessing.pool.Pool.imap` and
+:meth:`multiprocessing.pool.Pool.imap_unordered` to limit the number of
+submitted tasks whose results have not yet been yielded. If the buffer is
+full, iteration over the *iterables* pauses until a result is yielded from
+the buffer.