feat: add the section of the introduction to dynamic programming (#571)

* add the section of the introduction to
dynamic programming

* add a code comments.

codes/python/chapter_dynamic_programming/climbing_stairs_dfs.py

@@ -0,0 +1,28 @@
+"""
+File: climbing_stairs_dfs.py
+Created Time: 2023-06-30
+Author: Krahets (krahets@163.com)
+"""
+
+
+def dfs(i: int) -> int:
+    """搜索"""
+    # 已知 dp[1] 和 dp[2] ，返回之
+    if i == 1 or i == 2:
+        return i
+    # dp[i] = dp[i-1] + dp[i-2]
+    count = dfs(i - 1) + dfs(i - 2)
+    return count
+
+
+def climbing_stairs_dfs(n: int) -> int:
+    """爬楼梯：搜索"""
+    return dfs(n)
+
+
+"""Driver Code"""
+if __name__ == "__main__":
+    n = 9
+
+    res = climbing_stairs_dfs(n)
+    print(f"爬 {n} 阶楼梯共有 {res} 种方案")