Update README

README.md

@@ -1,3 +1,24 @@
 # KeychainWrapper
 
-A description of this package.
+A very simple wrapper around the iOS keychain.
+
+## Usage
+
+First instantiate `KeychainWrapper`, then use the instance to create, read or delete keychain entries, e.g.:
+
+```swift
+let keychainWrapper = KeychainWrapper(service: "myApp")
+
+// store password <-> username mapping for service "myApp"
+keychainWrapper["username"] = "secretPassword"
+
+// retrieve password for username
+let password = keychainWrapper["username"]
+
+// delete password entry for username in service "myApp"
+keychainWrapper["username"] = nil
+```
+
+## License
+
+See [LICENSE.md](LICENSE.md).