DOC: Add whatsnew note about fixing the bug of reading compressed UTF-16 file

Author: Licht-T

doc/source/whatsnew/v0.21.1.txt

@@ -76,7 +76,7 @@ I/O
 ^^^
 
 - Bug in class:`~pandas.io.stata.StataReader` not converting date/time columns with display formatting addressed (:issue:`17990`). Previously columns with display formatting were normally left as ordinal numbers and not converted to datetime objects.
-
+- Bug in :func:`read_csv` when reading the compressed UTF-16 file (:issue:`18071`)
 
 Plotting
 ^^^^^^^^