DOC: Document business frequency aliases (#17028)

Follow-up to gh-16978.

Author: gfyoung

doc/source/timeseries.rst

@@ -1093,9 +1093,9 @@ frequencies. We will refer to these aliases as *offset aliases*
     "QS", "quarter start frequency"
     "BQS", "business quarter start frequency"
     "A, Y", "year end frequency"
-    "BA", "business year end frequency"
+    "BA, BY", "business year end frequency"
     "AS, YS", "year start frequency"
-    "BAS", "business year start frequency"
+    "BAS, BYS", "business year start frequency"
     "BH", "business hour frequency"
     "H", "hourly frequency"
     "T, min", "minutely frequency"