add family tree to doc

Author: dabeng

README.md

@@ -165,6 +165,47 @@ You need the solution based on new datasource structure with **levelOffset data
 
 **compact data property** is designed for your use case. Once node data includes a "compact" prop with truthy value, itself and its descendant nodes will be arranged with compact mode.
 
+- [ I want to visualize genealogy/pedigree/family tree information](https://dabeng.github.io/OrgChart/family-tree.html)
+
+![family-tree](http://dabeng.github.io/OrgChart/img/family-tree.png)
+
+We use the following two-dimensional array datasource to build up the Family Tree.
+```
+      var datascource = [
+        [
+          { 'id': '8', 'name': 'Lao Ye', 'title': 'Grandfather', 'gender': 'male' },
+          { 
+            'id': '1', 'name': 'Lao Lao', 'title': 'Grandmother', 'gender': 'female', 'outsider': true,
+            'children': [
+              [
+                { 'id': '2', 'name': 'Bo miao', 'title': 'Aunt', 'gender': 'female'}
+              ],
+              [
+                { 'id': '3', 'name': 'Su Miao', 'title': 'Mother', 'gender': 'female',
+                  'children': [
+                    [
+                    
+                      { 'id': '12', 'name': 'Pang Pang', 'title': 'Wife', 'gender': 'female', 'outsider': true,
+                        'children': [
+                          [{ 'id': '7', 'name': 'Dan Dan', 'title': 'Daughter', 'gender': 'female' }],
+                          [{ 'id': '6', 'name': 'Er Dan', 'title': 'Daughter', 'gender': 'female' }],
+                        ]
+                      },
+                      { 'id': '5', 'name': 'Hei Hei', 'title': 'Me', 'gender': 'male' },
+                    ]
+                  ]
+                },
+                { 'id': '9', 'name': 'Tie Hua', 'title': 'Father', 'gender': 'male', 'outsider': true }
+              ],
+              [
+                { 'id': '10', 'name': 'Hong miao', 'title': 'Aunt', 'gender': 'female'}
+              ]
+            ]
+          }
+        ]
+      ];
+```
+
 ### how to start up demos locally
 
 - you have to install node.js v6+ because our unit tests are based on jsdom v11