Added "Network Reachability" section to the README.

README.md

@@ -1114,6 +1114,31 @@ Whether you need to set the `NSExceptionRequiresForwardSecrecy` to `NO` depends
 
 > It is recommended to always use valid certificates in production environments.
 
+### Network Reachability
+
+The `NetworkReachabilityManager` listens for reachability changes of hosts and addresses for both WWAN and WiFi network interfaces.
+
+```swift
+let manager = NetworkReachabilityManager(host: "www.apple.com")
+
+manager?.listener = { status in
+    print("Network Status Changed: \(status)")
+}
+
+manager?.startListening()
+```
+
+There are some important things to remember when using network reachability to determine what to do next.
+
+* **Do NOT** use Reachability to determine if a network request should be sent.
+  * You should **ALWAYS** send it.
+* When Reachability is restored, use the event to retry failed network requests.
+  * Even though the network requests may still fail, this is a good moment to retry them.
+* The network reachability status can be useful for determining why a network request may have failed.
+  * If a network request fails, it is more useful to tell the user that the network request failed due to being offline rather than a more technical errror, such as "request timed out."
+
+> It is recommended to check out [WWDC 2012 Session 706, "Networking Best Practices"](https://developer.apple.com/videos/play/wwdc2012-706/) for more info.
+
 ---
 
 ## Component Libraries