add example for async await into readme

Author: kitwtnb

README.md

@@ -288,6 +288,45 @@ storage.async.removeExpiredObjects() { result in
 }
 ```
 
+#### Swift Concurrency
+
+```swift
+do {
+  try await storage.async.setObject("Oslo", forKey: "my favorite city")
+  print("saved successfully")
+} catch {
+  print(error)
+}
+
+do {
+  let city = try await storage.async.object(forKey: "my favorite city")
+  print("my favorite city is \(city)")
+} catch {
+  print(error)
+}
+
+do {
+  let exists = try await storage.async.objectExists(forKey: "my favorite city")
+  if exists {
+    print("I have a favorite city")
+  }
+} catch {}
+
+do {
+  try await storage.async.remoeAll()
+  print("removal completes")
+} catch {
+  print(error)
+}
+
+do {
+  try await storage.async.removeExpiredObjects()
+  print("removal completes")
+} catch {
+  print(error)
+}
+```
+
 ### Expiry date
 
 By default, all saved objects have the same expiry as the expiry you specify in `DiskConfig` or `MemoryConfig`. You can overwrite this for a specific object by specifying `expiry` for `setObject`