cs: add «167. Two Sum II - Input Array Is Sorted»

URL:	https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/
Signed-off-by: Matej Focko <me@mfocko.xyz>

cs/two-sum-ii-input-array-is-sorted.cs

@@ -0,0 +1,15 @@
+public class Solution {
+    public int[] TwoSum(int[] numbers, int target) {
+        var (i, j) = (0, numbers.Length - 1);
+
+        while (i < j && numbers[i] + numbers[j] != target) {
+            if (numbers[i] + numbers[j] < target) {
+                ++i;
+            } else {
+                --j;
+            }
+        }
+
+        return new int[] { i + 1, j + 1 };
+    }
+}