doc(example): create template and the first case

Add case of data merging

Signed-off-by: Jiyong Huang <huangjy@emqx.io>

docs/directory.json

@@ -280,6 +280,22 @@
 			]
 		},
 		{
+			"title": "案例",
+			"path": "example/howto",
+			"children": [
+				{
+					"title": "数据合并",
+					"path": "example/data_merge/overview",
+					"children": [
+						{
+							"title": "合并单流多设备数据",
+							"path": "example/data_merge/merge_single_stream"
+						}
+					]
+				}
+			]
+		},
+		{
 			"title": "管理指南",
 			"children": [
 				{
@@ -959,6 +975,22 @@
 			]
 		},
 		{
+			"title": "Example",
+			"path": "example/howto",
+			"children": [
+				{
+					"title": "Data Merging",
+					"path": "example/data_merge/overview",
+					"children": [
+						{
+							"title": "Merge multiple devices' data in single stream",
+							"path": "example/data_merge/merge_single_stream"
+						}
+					]
+				}
+			]
+		},
+		{
 			"title": "Admin Guide",
 			"children": [
 				{

docs/en_US/example/data_merge/overview.md

@@ -0,0 +1,5 @@
+# Data Merging
+
+In IoT scenarios, devices such as sensors are often numerous in number. Data between multiple devices is correlated, and applications often need to acquire data from multiple devices in order to perform effective calculations. However, the data generated by each device is often reported independently. The huge amount of data makes data merging a challenge. This chapter introduces some typical data merging scenarios and explains how to use eKuiper for data merging.
+
+- [Merge multiple devices' data in single stream](./merge_single_stream.md)

docs/zh_CN/example/data_merge/overview.md

@@ -0,0 +1,5 @@
+# 数据合并
+
+在物联网场景中，终端设备如传感器往往数量众多。多个设备之间的数据是相关联的，应用通常需要获取多个设备的数据才能进行有效的计算。然而，每个设备产生的数据往往独立上报。巨大的数据量使得数据合并成为一个挑战。本章主要介绍一些数据合并的典型场景，讲解如何使用 eKuiper 进行数据合并。
+
+- [单流多设备合并场景](./merge_single_stream.md)