feat: add example

README.md

@@ -1,5 +1,34 @@
 # aes-gcm-stream
 
+## Encrypt
+
+```rust
+    // IMPORTANT! key and nonce SHOULD generate by random
+    let mut key = [0u8; 32];
+    let mut nonce = [0; 12];
+
+    let mut encryptor = Aes256GcmStreamEncryptor::new(key.clone(), &nonce);
+
+    let mut ciphertext = vec![];
+    ciphertext.extend_from_slice(&encryptor.update(b"Hello "));
+    ciphertext.extend_from_slice(&encryptor.update(b" World"));
+    ciphertext.extend_from_slice(&encryptor.update(b"!"));
+    let (last_block, tag) = encryptor.finalize();
+    ciphertext.extend_from_slice(&last_block);
+    ciphertext.extend_from_slice(&tag);
+
+    println!("Ciphertext: {}", hex::encode(&ciphertext));
+```
+
+## Run Example
+
+```shell
+$ cargo run --example encrypt_and_decrypt
+    Finished dev [unoptimized + debuginfo] target(s) in 0.10s
+     Running `target/debug/examples/encrypt_and_decrypt`
+Ciphertext: 86c22c5122404b39683ca9b79b889fd00a6212d1be2ebc3f4f8f22f90b
+Plaintext: Hello  World!
+```
 
 
 > Thanks: https://developer.aliyun.com/article/952809