Update README.md

Author: harshadbhere

Binary Tree/Minimum Depth of N-ary Tree/README.md

@@ -4,14 +4,14 @@ Given a binary tree, find its minimum depth.
 
 The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node. 
 
-###Example 1:
+### Example 1:
 
-![]https://assets.leetcode.com/uploads/2020/10/12/ex_depth.jpg
+![](https://assets.leetcode.com/uploads/2020/10/12/ex_depth.jpg)
 ```
 Input: root = [3,9,20,null,null,15,7]
 Output: 2
 ```
-###Constraints:
+### Constraints:
 
 - The number of nodes in the tree is in the range [0, 105].
 - -1000 <= Node.val <= 1000