copy subset of Sprig template functions

docs/sprig/date.md

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+# Date Functions
+
+## now
+
+The current date/time. Use this in conjunction with other date functions.
+
+## ago
+
+The `ago` function returns duration from time.Now in seconds resolution.
+
+```
+ago .CreatedAt
+```
+
+returns in `time.Duration` String() format
+
+```
+2h34m7s
+```
+
+## date
+
+The `date` function formats a date.
+
+Format the date to YEAR-MONTH-DAY:
+
+```
+now | date "2006-01-02"
+```
+
+Date formatting in Go is a [little bit different](https://pauladamsmith.com/blog/2011/05/go_time.html).
+
+In short, take this as the base date:
+
+```
+Mon Jan 2 15:04:05 MST 2006
+```
+
+Write it in the format you want. Above, `2006-01-02` is the same date, but
+in the format we want.
+
+## dateInZone
+
+Same as `date`, but with a timezone.
+
+```
+dateInZone "2006-01-02" (now) "UTC"
+```
+
+## duration
+
+Formats a given amount of seconds as a `time.Duration`.
+
+This returns 1m35s
+
+```
+duration "95"
+```
+
+## durationRound
+
+Rounds a given duration to the most significant unit. Strings and `time.Duration`
+gets parsed as a duration, while a `time.Time` is calculated as the duration since.
+
+This return 2h
+
+```
+durationRound "2h10m5s"
+```
+
+This returns 3mo
+
+```
+durationRound "2400h10m5s"
+```
+
+## unixEpoch
+
+Returns the seconds since the unix epoch for a `time.Time`.
+
+```
+now | unixEpoch
+```
+
+## dateModify, mustDateModify
+
+The `dateModify` takes a modification and a date and returns the timestamp.
+
+Subtract an hour and thirty minutes from the current time:
+
+```
+now | date_modify "-1.5h"
+```
+
+If the modification format is wrong `dateModify` will return the date unmodified. `mustDateModify` will return an error otherwise.
+
+## htmlDate
+
+The `htmlDate` function formats a date for inserting into an HTML date picker
+input field.
+
+```
+now | htmlDate
+```
+
+## htmlDateInZone
+
+Same as htmlDate, but with a timezone.
+
+```
+htmlDateInZone (now) "UTC"
+```
+
+## toDate, mustToDate
+
+`toDate` converts a string to a date. The first argument is the date layout and
+the second the date string. If the string can't be convert it returns the zero
+value.
+`mustToDate` will return an error in case the string cannot be converted.
+
+This is useful when you want to convert a string date to another format
+(using pipe). The example below converts "2017-12-31" to "31/12/2017".
+
+```
+toDate "2006-01-02" "2017-12-31" | date "02/01/2006"
+```