Update day13.md (#761)

Author: jportway

docs/2024/puzzles/day13.md

@@ -215,6 +215,7 @@ def part2(input: String): Long =
 - [Solution](https://github.com/Philippus/adventofcode/blob/main/src/main/scala/adventofcode2024/Day13.scala) by [Philippus Baalman](https://github.com/philippus)
 - [Solution](https://github.com/jnclt/adventofcode2024/blob/main/day13/claw-contraption.sc) by [jnclt](https://github.com/jnclt)
 - [Solution](https://github.com/TheDrawingCoder-Gamer/adventofcode2024/blob/master/src/main/scala/Day13.scala) by [Bulby](https://github.com/TheDrawingCoder-Gamer)
+- [Solution](https://github.com/jportway/advent2024/blob/master/src/main/scala/Day13.scala) by [Joshua Portway](https://github.com/jportway)
 
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