Clean up urlopen doc string.

Clarifies what is returned when and that the methods are common between the two.

Patch by Alexander Liu as part of #22797.
diff --git a/Misc/ACKS b/Misc/ACKS
index 8437805..ee67e27 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -884,6 +884,7 @@
 Gregor Lingl
 Everett Lipman
 Mirko Liss
+Alexander Liu
 Nick Lockwood
 Stephanie Lockwood
 Martin von Löwis