Added English wantagent

Signed-off-by: Nwusongqing <wusongqing@huawei.com>

en/application-dev/ability/wantagent.md

+# WantAgent Development
+### Introduction
+The **WantAgent** class encapsulates a **Want** object that specifies a particular action. To trigger a **WantAgent**, you can either call **wantAgent.trigger** to trigger it directly or add it to a notification so that it will be triggered when users tap the notification.
+
+You can use a **WantAgent** in a notification to start an ability or publish a common event.
+
+### When to Use
+Start another ability through a **WantAgent**.
+
+### Available APIs
+| API                                                                                         | Description|
+| ---------------------------------------------------------------------------------------------- | ----------- |
+| wantAgent.getWantAgentInfo(info: WantAgentInfo, callback: AsyncCallback\<WantAgent\>) | Creates a **WantAgent** object. This API uses an asynchronous callback to return the result.|
+| wantAgent.getWantAgent(info: WantAgentInfo): Promise\<WantAgent\>; | Creates a **WantAgent** object. This API uses a promise to return the result.|
+| commonEvent.trigger(agent: WantAgent, triggerInfo: TriggerInfo, callback?: Callback\<CompleteData\>) | Triggers a **WantAgent**.|
+
+### How to Develop
+1. Import the **WantAgent** module.
+
+```javascript
+import wantAgent from '@ohos.wantAgent';
+```
+
+2. Create a **WantAgentInfo** object. For details about the data types and parameters of **WantAgentInfo**, see [WantAgent Module](../reference/apis/js-apis-wantAgent.md#WantAgentInfo).
+
+```javascript
+private wantAgentObj = null	// Save the WantAgent object created. It will be used to complete the trigger operations.
+
+//wantAgentInfo
+var wantAgentInfo = {
+    wants: [
+        {
+            deviceId: "",
+            bundleName: "com.example.test",
+            abilityName: "com.example.test.MainAbility",
+            action: "",
+            entities: [],
+            uri: "",
+            parameters: {}
+        }
+    ],
+    operationType: OperationType.START_ABILITY,
+    requestCode: 0,
+    wantAgentFlags:[WantAgentFlags.CONSTANT_FLAG]
+}
+```
+
+3. Create a **WantAgent** object and save the returned **wantAgentObj** for subsequent trigger operations.
+
+```javascript
+// Create a WantAgent object.
+wantAgent.getWantAgent(wantAgentInfo, (err, wantAgentObj) => {
+    if (err.code) {
+        console.error("[WantAgent]getWantAgent err=" + JSON.stringify(err))
+    } else {
+        console.log("[WantAgent]getWantAgent success")
+        this.wantAgentObj = wantAgentObj
+    }
+})
+```
+
+4. Trigger the **WantAgent**.
+
+```
+// Trigger the WantAgent.
+var triggerInfo = {
+    code:0
+}
+wantAgent.trigger(wantAgentObj, triggerInfo, (completeData) => {
+    console.log("[WantAgent]getWantAgent success, completeData: ",  + JSON.stringify(completeData))
+})
+```