Update day01.md (#846)

Day 1 solution by merlin.

Author: merlinorg

docs/2025/puzzles/day01.md

@@ -8,5 +8,7 @@ https://adventofcode.com/2025/day/1
 
 ## Solutions from the community
 
+- [Solution](https://github.com/merlinorg/advent-of-code/blob/main/src/main/scala/year2025/day01.scala) by [merlinorg](https://github.com/merlinorg)
+
 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)