Update day12.md (#726)

Add Day12 solution by Alex Mc'key

docs/2024/puzzles/day12.md

@@ -377,6 +377,7 @@ def part2(input: String): Int = {
 - [Solution](https://github.com/makingthematrix/AdventOfCode2024/blob/main/src/main/scala/io/github/makingthematrix/AdventofCode2024/DayTwelve.scala) by [Maciej Gorywoda](https://github.com/makingthematrix)
 - [Solution](https://github.com/spamegg1/aoc/blob/master/2024/12/12.worksheet.sc#L191) by [Spamegg](https://github.com/spamegg1/)
 - [Solution](https://github.com/jnclt/adventofcode2024/blob/main/day12/garden-groups.sc) by [jnclt](https://github.com/jnclt)
+- [Solution](https://github.com/AlexMckey/AoC2024_Scala/blob/master/src/year2024/day12.scala) by [Alex Mc'key](https://github.com/AlexMckey)
 
 Share your solution to the Scala community by editing this page.
 You can even write the whole article! [See here for the expected format](https://github.com/scalacenter/scala-advent-of-code/discussions/424)