docs: add docs for getNeighbors

docs/api/Graph.en.md

@@ -1548,6 +1548,23 @@ const elements: {
 } = graph.getComboChildren('combo1')
 ```
 
+### getNeighbors(node, type)
+
+**Parameters**
+
+| Name    | Type  | Required | Description      |
+| ------- | ------ | -------- | ----------- |
+| node | string / INode | true    | node ID or the node instance |
+| type |  'source' / 'target' / undefined | false    | The type of the neighbors, 'source': only return the source nodes; 'target': only return the target nodes, undefined: return all of the neighbors |
+
+**Return**
+- Type of the return value: Array;
+- Return a list of node items.
+
+**Usage**
+``` javascript
+const neighbors = graph.getNeighbors('node1', 'source')
+```
 
 ## Coordinate Transformation
 
@@ -1689,12 +1706,12 @@ Get the in-degree, out-degree, degree, or all of the three kinds of degree.
 graph.getNodeDegree('node1', 'in');
 ```
 
-### getShortestPathMatrix
+### getShortestPathMatrix(cache, directed)
 Get all-pairs shortest-path matrix of the graph.
 
 **Parameters**
 
-| 名称    | 类型   | 是否必选 | 描述    |
+| Name    | Type  | Required | Description |
 | -------| ------ | -------- | ------- |
 | cache | boolean | false     | Whether to use the cached matrix, 'true' by default. |
 | directed | boolean | false     | Whether the graph is directed,  use the value of `graph.get('directed')` by default. | 
@@ -1704,12 +1721,12 @@ Get all-pairs shortest-path matrix of the graph.
 const matrix = graph.getShortestPathMatrix();
 ```
 
-### getAdjMatrix
+### getAdjMatrix(cache, directed)
 Get the adjacency matrix of the graph.
 
 **Parameters**
 
-| 名称    | 类型   | 是否必选 | 描述    |
+| Name    | Type  | Required | Description |
 | -------| ------ | -------- | ------- |
 | cache | boolean | false  | Whether to use the cached matrix, 'true' by default. |
 | directed | boolean | false  | Whether the graph is directed,  use the value of `graph.get('directed')` by default. |

docs/api/Graph.zh.md

@@ -1538,6 +1538,26 @@ const elements: {
 } = graph.getComboChildren('combo1')
 ```
 
+### getNeighbors(node, type)
+
+**参数**
+
+| 名称    | 类型   | 是否必选 | 描述        |
+| ------- | ------ | -------- | ----------- |
+| node | string / INode | true    | 节点 ID 或节点实例 |
+| type |  'source' / 'target' / undefined | false    | 邻居类型， 'source' 只获取当前节点的源节点，'target' 只获取当前节点指向的目标节点， 若不指定则返回所有类型的邻居 |
+
+**返回值**
+
+- 返回值类型：Array；
+- 返回值符合要求的节点数组。
+
+**用法**
+
+``` javascript
+const neighbors = graph.getNeighbors('node1', 'source')
+```
+
 ## 坐标转换
 
 这部分主要是说明视口坐标、Canvas 坐标和页面坐标之前的相互转换。其中视口坐标和 Canvas 坐标的示意图如下所示。
@@ -1677,7 +1697,7 @@ graph.stopAnimate();
 graph.getNodeDegree('node1', 'in');
 ```
 
-### getShortestPathMatrix
+### getShortestPathMatrix(cache, directed)
 获取图中两两节点之间的最短路径矩阵。
 
 **参数**
@@ -1696,7 +1716,7 @@ graph.getNodeDegree('node1', 'in');
 const matrix = graph.getShortestPathMatrix();
 ```
 
-### getAdjMatrix
+### getAdjMatrix(cache, directed)
 获取邻接矩阵。
 
 **参数**

docs/api/nodeEdge/Node.en.md

@@ -45,6 +45,23 @@ const node = graph.findById('node');
 const hasLocked = node.hasLocked();
 ```
 
+### getNeighbors(type)
+
+**Parameters**
+
+| Name    | Type  | Required | Description      |
+| ------- | ------ | -------- | ----------- |
+| type |  'source' / 'target' / undefined | false    | The type of the neighbors, 'source': only return the source nodes; 'target': only return the target nodes, undefined: return all of the neighbors |
+
+**Return**
+- Type of the return value: Array;
+- Return a list of node items.
+
+**Usage**
+``` javascript
+const neighbors = node.getNeighbors('source')
+```
+
 ## getEdges()
 
 Get the related edges (the node is the source or the target of the edge) of the node.

docs/api/nodeEdge/Node.zh.md

@@ -51,6 +51,25 @@ const node = graph.findById('node');
 const hasLocked = node.hasLocked();
 ```
 
+## getNeighbors(type)
+
+**参数**
+
+| 名称    | 类型   | 是否必选 | 描述        |
+| ------- | ------ | -------- | ----------- |
+| type |  'source' / 'target' / undefined | false    | 邻居类型， 'source' 只获取当前节点的源节点，'target' 只获取当前节点指向的目标节点， 若不指定则返回所有类型的邻居 |
+
+**返回值**
+
+- 返回值类型：Array；
+- 返回值符合要求的节点实例数组。
+
+**用法**
+
+``` javascript
+const neighbors = node.getNeighbors('source')
+```
+
 ## getEdges()
 
 获取与当前节点有关联的所有边。