feat: update readme

README.md

@@ -2,3 +2,21 @@
 
 PENGING...
 
+
+BC test code:
+```java
+public static void encryptGcmNoPadding(String key, String data, String nonce, String associatedData) throws Exception {
+    Cipher cipher = Cipher.getInstance("SM4/GCM/NoPadding", BouncyCastleProvider.PROVIDER_NAME);
+    Key sm4Key = new SecretKeySpec(Bytes.fromHex(key).bytes(), "SM4");
+    byte[] iv = Bytes.fromHex(nonce).bytes();
+    GCMParameterSpec s = new GCMParameterSpec(128, iv);
+    cipher.init(Cipher.ENCRYPT_MODE, sm4Key, s);
+    if (associatedData != null && associatedData.length() > 0) {
+        cipher.updateAAD(Bytes.fromHex(associatedData).bytes());
+    }
+    byte[] aa = cipher.doFinal(data.getBytes(StandardCharsets.UTF_8));
+    System.out.println(Bytes.from(aa).asHex());
+}
+```
+
+