Update README.md

README.md

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 # DateFormatter
 A small framwork for transforming Dates to Strings, and Strings to Dates
+
+DateFormatter is a small library for transforming strings to dates, and dates to strings. The library uses a relativley unknown class in Foundation called [NSValueTransformer](http://nshipster.com/nsvaluetransformer/). This class is meant to be used to transform one value to another, and be subclassed to support transforming your types.
+
+## Installation
+
+### Carthage
+
+Copy and paste the following into your `Cartfile`
+```
+github "Chandlerdea/DateTransformer"
+```
+
+### Manual
+
+You can just drop DateTransformer.xcodeproj into your project and then add DateTransformer.framework to your app’s embedded frameworks.
+
+## Use
+
+There are two `NSValueTransformer` subclasses you can use, `StringToDateTransformer` and `TimeIntervalToStringTransformer`. 
+
+### StringToDateTransformer
+
+This class's forward transformation type is `Date`, and it allows reverse transformatio. That means that you can either take a `String` and transform it into a `Date`, or vice versa. This can be useful for taking string representaions of dates from an api and transform them into `Date` objects. By default, the class uses the format `yyyy-MM-dd'T'HH:mm:ssZ` to create dates. So if your api sends date strings in a different format, you'll have to pass the custom format to the date transformer.  Here's an example using a custom format:
+
+```
+let someApiData: [String: String] = ....
+let createdAtString: String = someApiData["created_at"]!
+let transformer: StringToDateTransformer = StringToDateTransformer()
+let dateFormat: String = "EEEE, MMM d, yyyy"
+if let createdAt: Date = transformer.transformString(createdAtString, dateFormat: dateFormat) {
+  // do something with the date
+}
+```
+
+You can also do reverse transformations, from `Date` to `String`. By default, the class uses the format `EEEE, MMM d, yyyy` to create the date strings. It is also important to note that the passed in date will have the system time zone applied by default. There is a `timeZone` argument that allows you to pass a custom time zone that will be applied to the date. Here's an example: 
+
+```
+let date: Date = Date(timeIntervalSince1970: 0)
+let format: String = "MM/dd/yyyy"
+let transformer: StringToDateTransformer = StringToDateTransformer()
+if let result: String = transformer.transformDate(date, dateFormat: format) {
+  // "01/01/1970"
+}
+```
+
+### TimeIntervalToStringTransformer
+
+`TimeIntervalToStringTransformer` transforms a `TimeInerval` to a `String`. A usecase would be if you were counting down from a date in the future to now, and you wanted to display the number of hours, minutes, and seconds to the user. The default format used by the class is `EEEE, MMM d, yyyy`. As before, it is important to note that the passed in timeInterval will have the system time zone applied by default. There is a `timeZone` argument that allows you to pass a custom time zone that will be applied to the date Here's an example:
+
+```
+let secondsToFutureDate: TimeInterval = ...
+let dateFormat: String = "HH:mm:ss"
+let transformer: TimeIntervalToStringTransformer = TimeIntervalToStringTransformer(dateFormat: dateFormat)
+if let countdownString: String = transformer.transformTimeInterval(secondsToFutureDate) {
+  // "01:01:01"
+}
+
+```
+
+## Support
+
+If you find any bugs, or have any critiques, please open a PR and I will fix them as soon as I can. And if you feel the need to add some more tests, you're more than welcome!