feat: add the problem link

jtr109 · jtr109 · commit f485c6ec37a1 · 2021-05-04T21:11:19.000+08:00
diff --git a/non_decreasing_array/src/lib.rs b/non_decreasing_array/src/lib.rs
@@ -1,3 +1,7 @@
+/*
+ * https://leetcode.com/explore/challenge/card/may-leetcoding-challenge-2021/598/week-1-may-1st-may-7th/3731/
+ */
+
 pub struct Solution {}
 
 impl Solution {
