Update README for problem 53

Author: anirudhology

README.md

@@ -32,6 +32,7 @@ LeetCode solutions in Python
 | 49         | Group Anagrams                                            | [Solution](problems/string/group_anagrams.py)                                              | Medium     | String, Hashing                       |
 | 50         | Pow (x, n)                                                | [Solution](problems/math/pow_xn.py)                                                        | Medium     | Math                                  |
 | 51         | N Queens                                                  | [Solution](problems/backtracking/n_queens.py)                                              | Hard       | Backtracking                          |
+| 53         | Maximum Subarray                                          | [Solution](problems/dynamic_programming/maximum_subarray.py)                               | Medium     | Dynamic Programming                   |
 | 54         | Spiral Matrix                                             | [Solution](problems/matrix/spiral_matrix.py)                                               | Medium     | Matrix                                |
 | 56         | Merge Intervals                                           | [Solution](problems/intervals/merge_intervals.py)                                          | Medium     | Intervals, Array                      |
 | 57         | Insert Interval                                           | [Solution](problems/intervals/insert_interval.py)                                          | Medium     | Intervals, Array                      |