Add markdown images demo.

Author: Shammamah Hossain

demo/data.ts

@@ -154,6 +154,12 @@ export const generateMarkdownMockData = (rows: number) => unpackIntoColumnsAndDa
             '```python',
             'def hello_table(' + i + '):',
             '  print("hello, " + i)'].join('\n'), rows)
+    },
+    {
+        id: 'markdown-images',
+        name: ['', 'Images'],
+        presentation: 'markdown',
+        data: gendata(i => '![image ' + i + ' alt text](https://dash.plot.ly/assets/images/logo.png)')
     }
 
 ]);