Add documentation on how to sort in reverse order

doc/ledger.1

@@ -214,6 +214,9 @@ Note that a comma-separated list of expressions is allowed, in which case each
 sorting term is used in order to determine the final ordering.  For example,
 to search by date and then amount, one would use:
 .Dl ledger reg --sort 'date, amount'
+The sort order may be controlled with the '-' sign. For example, to sort in
+reverse chronological order:
+.Dl ledger reg --sort '-date'
 .It Fl \-tail Ar number
 Only show the last
 .Ar number