chore: add package level comments

solutions/21/q2130/solution.go

@@ -1,3 +1,4 @@
+// Package q2130 implements a solution for https://leetcode.com/problems/maximum-twin-sum-of-a-linked-list/
 package q2130
 
 import "math"

solutions/21/q2154/solution.go

@@ -1,3 +1,4 @@
+// Package q2154 implements a solution for https://leetcode.com/problems/keep-multiplying-found-values-by-two/
 package q2154
 
 import "slices"

solutions/21/q2169/solution.go

@@ -1,3 +1,4 @@
+// Package q2169 implements a solution for https://leetcode.com/problems/count-operations-to-obtain-zero/
 package q2169
 
 func countOperations(num1 int, num2 int) int {