Added README.md file for Shift 2D Grid

Author: achuatchaya

1386-shift-2d-grid/README.md

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+<h2><a href="https://leetcode.com/problems/shift-2d-grid">Shift 2D Grid</a></h2> <img src='https://img.shields.io/badge/Difficulty-Easy-brightgreen' alt='Difficulty: Easy' /><hr><p>Given a 2D <code>grid</code> of size <code>m x n</code>&nbsp;and an integer <code>k</code>. You need to shift the <code>grid</code>&nbsp;<code>k</code> times.</p>
+
+<p>In one shift operation:</p>
+
+<ul>
+	<li>Element at <code>grid[i][j]</code> moves to <code>grid[i][j + 1]</code>.</li>
+	<li>Element at <code>grid[i][n - 1]</code> moves to <code>grid[i + 1][0]</code>.</li>
+	<li>Element at <code>grid[m&nbsp;- 1][n - 1]</code> moves to <code>grid[0][0]</code>.</li>
+</ul>
+
+<p>Return the <em>2D grid</em> after applying shift operation <code>k</code> times.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2019/11/05/e1.png" style="width: 400px; height: 178px;" />
+<pre>
+<strong>Input:</strong> <code>grid</code> = [[1,2,3],[4,5,6],[7,8,9]], k = 1
+<strong>Output:</strong> [[9,1,2],[3,4,5],[6,7,8]]
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2019/11/05/e2.png" style="width: 400px; height: 166px;" />
+<pre>
+<strong>Input:</strong> <code>grid</code> = [[3,8,1,9],[19,7,2,5],[4,6,11,10],[12,0,21,13]], k = 4
+<strong>Output:</strong> [[12,0,21,13],[3,8,1,9],[19,7,2,5],[4,6,11,10]]
+</pre>
+
+<p><strong class="example">Example 3:</strong></p>
+
+<pre>
+<strong>Input:</strong> <code>grid</code> = [[1,2,3],[4,5,6],[7,8,9]], k = 9
+<strong>Output:</strong> [[1,2,3],[4,5,6],[7,8,9]]
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>m ==&nbsp;grid.length</code></li>
+	<li><code>n ==&nbsp;grid[i].length</code></li>
+	<li><code>1 &lt;= m &lt;= 50</code></li>
+	<li><code>1 &lt;= n &lt;= 50</code></li>
+	<li><code>-1000 &lt;= grid[i][j] &lt;= 1000</code></li>
+	<li><code>0 &lt;= k &lt;= 100</code></li>
+</ul>