diff --git a/Gif/RRuleSwiftExample.gif b/Gif/RRuleSwiftExample.gif
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diff --git a/LICENSE.md b/LICENSE.md
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+The MIT License (MIT)
+
+Copyright (c) 2016 Teambition
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
\ No newline at end of file
diff --git a/README.md b/README.md
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+#RRuleSwift
+Swift library for working with recurrence rules of calendar dates.
+
+![Example](Gif/RRuleSwiftExample.gif "RRuleSwiftExample")
+
+RRuleSwift is based on [rrule.js](https://github.com/jkbrzt/rrule).
+
+##How To Get Started
+###Carthage
+Specify "RRuleSwift" in your Cartfile:
+```ogdl 
+github "teambition/RRuleSwift"
+```
+
+###Usage
+##### Initialization
+```swift
+var recurrenceRule = RecurrenceRule(recurrenceWithFrequency: .Daily)
+recurrenceRule.calendar = ...
+recurrenceRule.frequency = ...
+recurrenceRule.interval = ...
+recurrenceRule.firstDayOfWeek = ...
+recurrenceRule.startDate = ...
+recurrenceRule.recurrenceEnd = ...
+recurrenceRule.bysetpos = ...
+recurrenceRule.byyearday = ...
+recurrenceRule.bymonth = ...
+recurrenceRule.byweekno = ...
+recurrenceRule.bymonthday = ...
+recurrenceRule.byweekday = ...
+recurrenceRule.byhour = ...
+recurrenceRule.byminute = ...
+recurrenceRule.bysecond = ...
+```
+
+#####  Rule form string
+```swift
+let ruleString = "RRULE:FREQ=MONTHLY;DTSTART=20160404T021000Z;COUNT=5;INTERVAL=2;WKST=MO;BYDAY=MO,TU"
+let rule = RecurrenceRule.ruleWithString(ruleString)
+```
+
+#####  String form rule
+```swift
+let ruleString = rule.toRRuleString()
+print(ruleString)
+// RRULE:FREQ=MONTHLY;DTSTART=20160404T021000Z;COUNT=5;INTERVAL=2;WKST=MO;BYDAY=MO,TU
+```
+
+##### Occurrence generator
+```swift
+let ruleString = "RRULE:FREQ=YEARLY;COUNT=5;WKST=MO"
+if let rule = RecurrenceRule.ruleWithString(ruleString) {
+    let allDates = rule.allOccurrences()
+    print(allDates)
+    /*
+    2016-04-06 14:26:17 Wed, 
+    2017-04-06 14:26:17 Thu, 
+    2018-04-06 14:26:17 Fri, 
+    2019-04-06 14:26:17 Sat, 
+    2020-04-06 14:26:17 Mon
+    */
+
+    let date = dateFormatter.dateFromString("2017-01-01 00:00:00 Sun")
+    let otherDate = dateFormatter.dateFromString("2020-01-01 00:00:00 Wed")
+    let betweenDates = rule.occurrencesBetween(date: date!, andDate: otherDate!)
+    print(betweenDates)
+    /*
+    2017-04-06 14:26:17 Thu, 
+    2018-04-06 14:26:17 Fri, 
+    2019-04-06 14:26:17 Sat
+    */
+}
+```
+
+## Minimum Requirement
+iOS 8.0
+
+## Release Notes
+* [Release Notes](https://github.com/teambition/RRuleSwift/releases)
+
+## License
+RRuleSwift is released under the MIT license. See [LICENSE](https://github.com/teambition/RRuleSwift/blob/master/LICENSE.md) for details.
+
+## More Info
+Have a question? Please [open an issue](https://github.com/teambition/RRuleSwift/issues/new)!
diff --git a/RRuleSwift/RecurrenceRule.swift b/RRuleSwift/RecurrenceRule.swift
index cf44e03..e0681b6 100644
--- a/RRuleSwift/RecurrenceRule.swift
+++ b/RRuleSwift/RecurrenceRule.swift
@@ -14,7 +14,7 @@ public struct RecurrenceRule {
     public var calendar = NSCalendar.currentCalendar()
 
     /// The frequency of the recurrence rule.
-    public var frequency: RecurrenceFrequency!
+    public var frequency: RecurrenceFrequency
 
     /// Specifies how often the recurrence rule repeats over the unit of time indicated by its frequency. For example, a recurrence rule with a frequency type of RecurrenceFrequency.Weekly and an interval of 2 repeats every two weeks.
     ///
diff --git a/RRuleSwiftExample/RRuleExampleViewController.swift b/RRuleSwiftExample/RRuleExampleViewController.swift
index 93dd881..fc8e9a6 100644
--- a/RRuleSwiftExample/RRuleExampleViewController.swift
+++ b/RRuleSwiftExample/RRuleExampleViewController.swift
@@ -340,7 +340,7 @@ extension RRuleExampleViewController: UIPickerViewDataSource, UIPickerViewDelega
     func pickerView(pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
         switch pickerView.tag {
         case 0:
-            rule.frequency = kFrequenciesDic[kFrequencies[row]]
+            rule.frequency = kFrequenciesDic[kFrequencies[row]]!
         case 1:
             rule.interval = row + 1
         case 2: