Add news file entry for change.

iUnknwn · pitrou · commit 3fa038e66e68 · 2019-05-22T22:54:15.000+02:00
diff --git a/Misc/NEWS.d/next/Library/2018-04-04-14-54-30.bpo-24882.urybpa.rst b/Misc/NEWS.d/next/Library/2018-04-04-14-54-30.bpo-24882.urybpa.rst
@@ -0,0 +1 @@
+Change ThreadPoolExecutor to use existing idle threads before spinning up new ones.

Original file line number	Diff line number	Diff line change
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	`1`	`+Change ThreadPoolExecutor to use existing idle threads before spinning up new ones.`