chore: Added a README

README.md

@@ -2,3 +2,87 @@
 
 <a href="https://swift.org" target="_blank"><img src="https://img.shields.io/badge/Language-Swift4-orange.svg" alt="Language Swift 4"></a>
 [![Build Status](https://app.bitrise.io/app/75f1a12b7326ea09/status.svg?token=-Wus-j9Iq8IVKcFB3wLhSg&branch=master)](https://app.bitrise.io/app/75f1a12b7326ea09)
+
+BufferedLogger is a tiny but thread-safe logger with a buffering and retrying mechanism for iOS.
+
+- Buffer log entries until it's time to output them.
+- Batch multiple log entries to use them at the same time.
+- Retry outputing log entries when some backoff time elapsed after some errors occurred.
+
+You can use this framework...
+
+- To send a group of log entries to your server.
+- To resend them when some errors like a networking trouble is occured.
+
+## Installation
+
+### Carthage
+
+```
+github "yoheimuta/BufferedLogger"
+```
+## Usage
+
+For details, refer to a [Demo project](https://github.com/yoheimuta/BufferedLogger/tree/master/Demo).
+
+### Define your own Writer
+
+Posted log entries are buffered and emitted as a chunk on a routine schedule.
+
+write method is ensured to call serially, which means it is run by a serial queue.
+
+```swift
+class MyWriter: Writer {
+    func write(_ chunk: Chunk, completion: (Bool) -> Void) {
+        // You can implement something useful like uploading logs to your server.
+        print("chunk is \(chunk)")
+
+        chunk.entries.forEach {
+            print("entry is \($0)")
+        }
+
+        completion(true)
+    }
+}
+```
+
+### Make the logger and post a log
+
+You have to register your writer to the logger and can post your log with it from any thread.
+
+A call to post method is no blocking.
+
+```swift
+import BufferedLogger
+
+logger = BFLogger(writer: MyWriter())
+logger.post("1".data(using: .utf8)!)
+logger.post("2".data(using: .utf8)!)
+logger.post("3".data(using: .utf8)!)
+```
+
+You can also create your configuration for buffering and emitting mechanism.
+
+If you omit to define your configuration, default below is used. Each meaning is in a protocol comment.
+
+```swift
+public static let `default` = Config(flushEntryCount: 5,
+                                     flushInterval: 10,
+                                     retryRule: DefaultRetryRule(retryLimit: 3))
+
+public class DefaultRetryRule: RetryRule {
+    public let retryLimit: Int
+
+    public init(retryLimit: Int) {
+        self.retryLimit = retryLimit
+    }
+
+    public func delay(try count: Int) -> TimeInterval {
+        return 2.0 * pow(2.0, Double(count - 1))
+    }
+}
+```
+
+## TODO
+
+- [ ] Stores the unsent entries in the local storage when the application couldn't send log entries.