Update changelog and README

README.markdown

@@ -614,6 +614,27 @@ ok
 %% that timezone to our intended timezone.
 ```
 
+## Date Arithmetic
+
+The current implementation of qdate's date arithmetic returns Unixtimes.
+
+There are 8 functions for date arithmetic:
+
+	+ `add_seconds(Seconds, Date)`
+	+ `add_minutes(Minutes, Date)`
+	+ `add_hours(Hours, Date)`
+	+ `add_days(Days, Date)`
+	+ `add_weeks(Weeks, Date)`
+	+ `add_months(Months, Date)`
+	+ `add_years(Years, Date)`
+	+ `add_date(DateToAdd, Date)` - `DateToAdd` is a shortcut way of adding
+	  numerous options. For example. `qdate:add_date({{1, 2, -3}, {-500, 20, 0}})`
+	  will add 1 year, add 2 months, subtract 3 days, subtract 500 hours, add 20
+	  minutes, and not make any changes to seconds.
+
+For the date arithmetic functions, `Date`, like all qdate functions, can be any
+format.
+
 ## Thanks
 
 A few shoutouts to [Dale Harvey](http://github.com/daleharvey) and the