Update README.md

add usege desc

README.md

@@ -8,8 +8,36 @@
 
 ## Usage
 
+Use this package as a library
+1. Depend on it
+Add this to your package's pubspec.yaml file:
+
+```
+dependencies:
+  flutter_aes_ecb_pkcs5: ^0.1.1
+```
+
+2. Install it You can install packages from the command line:
+
+with Flutter:
+
+```
+$ flutter pub get
+```
+
+Alternatively, your editor might support flutter pub get. Check the docs for your editor to learn more.
+
+3. Import it Now in your Dart code, you can use:
+
+```
+import 'package:flutter_aes_ecb_pkcs5/flutter_aes_ecb_pkcs5.dart';
+```
+
+
+
+#### AES Use Example
+
 
-#### AES
 
 ```dart
 import 'package:flutter_aes_ecb_pkcs5/flutter_aes_ecb_pkcs5.dart';
@@ -18,15 +46,15 @@ void main() {
 
     var data = "{\"username\":\"helloword\"}";
     
-    //生成16字节的随机密钥
+    //generate a 16-byte random key
     var key = await FlutterAesEcbPkcs5.generateDesKey(128);
     
     print(key);
-    //加密
+    //encrypt
     var encryptText = await FlutterAesEcbPkcs5.encryptString(data, key);
     
     print(encryptText);
-    //解密
+    //decrypt
     var decryptText  = await FlutterAesEcbPkcs5.decryptString(encryptText, key);
     
     print(decryptText);