Add solution for first task

Author: Neodelf

1/two_sum.rb

@@ -0,0 +1,10 @@
+# @param {Integer[]} nums
+# @param {Integer} target
+# @return {Integer[]}
+def two_sum(nums, target)
+    nums.each_with_index do |n, i|
+        number = target - n
+        index = nums[i+1..-1].index(number)
+        return [i, index+i+1] if index
+    end
+end