DOC: Add bz2 bugfix to changelog

Author: MilesCranmer

doc/source/whatsnew/v2.1.0.rst

@@ -449,6 +449,7 @@ I/O
 - Bug in :func:`read_html`, tail texts were removed together with elements containing ``display:none`` style (:issue:`51629`)
 - Bug in :func:`read_sql` when reading multiple timezone aware columns with the same column name (:issue:`44421`)
 - Bug when writing and reading empty Stata dta files where dtype information was lost (:issue:`46240`)
+- Bug where ``bz2`` was treated as a hard requirement (:issue:`53857`)
 
 Period
 ^^^^^^