[RIP-9] Add the introduction of the basic samples in RocketMQ (#758)

 [RIP-9] Add the introduction of the basic samples in RocketMQ

docs/en/Example_Simple.md

+# Basic Sample 
+------
+Two functions below are provided in the basic sample:
+* The RocketMQ can be utilized to send messages in three ways: reliable synchronous, reliable asynchronous, and one-way transmission.  The first two message types are reliable because there is a response whether they were sent successfully.
+* The RocketMQ can be utilized to consume messages.
+### 1 Add Dependency
+maven:
+``` java
+<dependency>
+  <groupId>org.apache.rocketmq</groupId>
+  <artifactId>rocketmq-client</artifactId>
+  <version>4.3.0</version>
+</dependency>
+```
+gradle: 
+``` java 
+compile 'org.apache.rocketmq:rocketmq-client:4.3.0'
+```
+### 2 Send Messages
+##### 2.1 Use Producer to Send Synchronous Messages
+Reliable synchronous transmission is used in extensive scenes, such as important notification messages, SMS notification.
+``` java
+public class SyncProducer {
+  public static void main(String[] args) throws Exception {
+    // Instantiate with a producer group name
+    DefaultMQProducer producer = new DefaultMQProducer("please_rename_unique_group_name");
+    // Specify name server addresses
+    producer.setNamesrvAddr("localhost:9876");
+    // Launch the producer instance
+    producer.start();
+    for (int i = 0; i < 100; i++) {
+      // Create a message instance with specifying topic, tag and message body
+      Message msg = new Message("TopicTest" /* Topic */,
+        "TagA" /* Tag */,
+        ("Hello RocketMQ " + i).getBytes(RemotingHelper.DEFAULT_CHARSET) /* Message body */
+        );
+      // Send message to one of brokers
+      SendResult sendResult = producer.send(msg);
+      // Check whether the message has been delivered by the callback of sendResult
+      System.out.printf("%s%n", sendResult);
+    }
+    // Shut down once the producer instance is not longer in use
+    producer.shutdown();
+  }
+}
+```
+##### 2.2 Send Asynchronous Messages
+Asynchronous transmission is generally used in response time sensitive business scenarios. It means that it is unable for the sender to wait the response of the Broker too long.
+``` java
+public class AsyncProducer {
+  public static void main(String[] args) throws Exception {
+    // Instantiate with a producer group name
+    DefaultMQProducer producer = new DefaultMQProducer("please_rename_unique_group_name");
+    // Specify name server addresses
+    producer.setNamesrvAddr("localhost:9876");
+    // Launch the producer instance
+    producer.start();
+    producer.setRetryTimesWhenSendAsyncFailed(0);
+    for (int i = 0; i < 100; i++) {
+      final int index = i;
+      // Create a message instance with specifying topic, tag and message body
+      Message msg = new Message("TopicTest",
+        "TagA",
+        "OrderID188",
+        "Hello world".getBytes(RemotingHelper.DEFAULT_CHARSET));
+      // SendCallback: receive the callback of the asynchronous return result.
+      producer.send(msg, new SendCallback() {
+        @Override
+        public void onSuccess(SendResult sendResult) {
+          System.out.printf("%-10d OK %s %n", index,
+            sendResult.getMsgId());
+        }
+        @Override
+        public void onException(Throwable e) {
+          System.out.printf("%-10d Exception %s %n", index, e);
+          e.printStackTrace();
+        }
+      });
+    }
+    // Shut down once the producer instance is not longer in use
+    producer.shutdown();
+  }
+}
+```
+##### 2.3 Send Messages in One-way Mode
+One-way transmission is used for cases requiring moderate reliability, such as log collection.
+``` java
+public class OnewayProducer {
+  public static void main(String[] args) throws Exception{
+    // Instantiate with a producer group name
+    DefaultMQProducer producer = new DefaultMQProducer("please_rename_unique_group_name");
+    // Specify name server addresses
+    producer.setNamesrvAddr("localhost:9876");
+    // Launch the producer instance
+    producer.start();
+    for (int i = 0; i < 100; i++) {
+      // Create a message instance with specifying topic, tag and message body
+      Message msg = new Message("TopicTest" /* Topic */,
+        "TagA" /* Tag */,
+        ("Hello RocketMQ " + i).getBytes(RemotingHelper.DEFAULT_CHARSET) /* Message body */
+      );
+      // Send in one-way mode, no return result
+      producer.sendOneway(msg);
+    }
+    // Shut down once the producer instance is not longer in use
+     producer.shutdown();
+  }
+}
+```
+### 3 Consume Messages
+``` java
+public class Consumer {
+  public static void main(String[] args) throws InterruptedException, MQClientException {
+    // Instantiate with specified consumer group name
+    DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("please_rename_unique_group_name");
+    
+    // Specify name server addresses
+    consumer.setNamesrvAddr("localhost:9876");
+
+    // Subscribe one or more topics and tags for finding those messages need to be consumed
+    consumer.subscribe("TopicTest", "*");
+    // Register callback to execute on arrival of messages fetched from brokers
+    consumer.registerMessageListener(new MessageListenerConcurrently() {
+      @Override
+      public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> msgs, ConsumeConcurrentlyContext context) {
+        System.out.printf("%s Receive New Messages: %s %n", Thread.currentThread().getName(), msgs);
+        // Mark the message that have been consumed successfully
+        return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
+      }
+    });
+    // Launch the consumer instance
+    consumer.start();
+    System.out.printf("Consumer Started.%n");
+  }
+}
+```
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