docs: Add doc for time template func

content/templates/functions.md

@@ -741,6 +741,16 @@ This can be useful if you want to use Gravatar for generating a unique avatar:
 ```
 
 
+## Times
+
+### time
+
+`time` converts a timestamp string into a [`time.Time`](https://godoc.org/time#Time) structure so you can access its fields. E.g.
+
+* `{{ time "2016-05-28" }}` → "2016-05-28T00:00:00Z"
+* `{{ (time "2016-05-28").YearDay }}` → 149
+* `{{ mul 1000 (time "2016-05-28T10:30:00.00+10:00").Unix }}` → 1464395400000 (Unix time in milliseconds)
+
 
 ## URLs