docs: add the README (#4)

README.md

@@ -1 +1,75 @@
-# kafka-casbin
+# kafka-casbin
+![License](https://img.shields.io/github/license/jcasbin/kafka-casbin)
+
+[Kafka](https://kafka.apache.org) authorization plugin based on Casbin.
+
+## Installation
+
+```
+git clone https://github.com/jcasbin/kafka-casbin.git
+```
+## Simple Example
+
+```java
+public class Main {
+
+    public static void main(String[] args) throws InstantiationException, IllegalAccessException {
+        // create the CasbinAuthorizer object.
+        CasbinAuthorizer authorizer = new CasbinAuthorizer();
+        Map<String, String> configs = new HashMap<>();
+        configs.put("casbin.authorizer.model", "examples/acl_model.conf");
+        configs.put("casbin.authorizer.policy", "examples/acl_policy.csv");
+        // Set the configs for the authorizer.
+        authorizer.configure(configs);
+
+        // You should create the real serverInfo object
+        AuthorizerServerInfo serverInfo = mock(AuthorizerServerInfo.class);
+        when(serverInfo.endpoints()).thenReturn(new ArrayList<>());
+        authorizer.start(serverInfo);
+
+        // create ResourcePattern
+        ResourcePattern TOPIC_RESOURCE = new ResourcePattern(
+                org.apache.kafka.common.resource.ResourceType.TOPIC,
+                "target_topic",
+                PatternType.LITERAL
+        );
+        Action action = new Action(AclOperation.READ, TOPIC_RESOURCE, 0, true, true);
+
+        // Check the permission.
+        List<AuthorizationResult> results =
+                authorizer.authorize(requestContext("User", "alice"),
+                        Arrays.asList(action));
+
+        for (AuthorizationResult result : results) {
+           if (result == AuthorizationResult.ALLOWED) {
+               System.out.println("有权限");
+           } else {
+               System.out.println("无权限");
+           }
+        }
+
+    }
+
+    private static AuthorizableRequestContext requestContext(String principalType, String name) {
+        return new RequestContext(
+                new RequestHeader(ApiKeys.METADATA, (short) 0, "test-client-id", 123),
+                "test-connection-id",
+                InetAddress.getLoopbackAddress(),
+                new KafkaPrincipal(principalType, name),
+                new ListenerName("PLAINTEXT"),
+                SecurityProtocol.PLAINTEXT,
+                ClientInformation.EMPTY,
+                false
+        );
+    }
+}
+```
+
+## Getting Help
+
+- [jCasbin](https://github.com/casbin/jCasbin)
+- [kafka-client](https://github.com/apache/kafka)
+
+## License
+
+This project is under Apache 2.0 License. See the [LICENSE](https://github.com/jcasbin/kafka-casbin/blob/master/LICENSE) file for the full license text.