Update README.md

added usage

Author: misino

README.md

@@ -1,4 +1,21 @@
-react-datepicker
-================
+#react-datepicker
 
-Datepicker component for application using Facebook React
+Datepicker component for applications based on Facebook React library.
+
+##Usage
+Standalone datepicker element. It can perform action if date is selected. Parameters are optional.
+
+```
+var callback = function(date) {
+  alert('new selected date is: '+date);
+}
+
+<Datepicker date={new Date()} onChangeDate={callback} show={true} />
+```
+
+This library contains own datepicker integration with input element.
+All parameters are optional.
+Default: date = new Date()
+```
+<DatepickerInput date={new Date()} />
+```