link to 2024 year from main readme

Author: dannyvankooten

README.md

@@ -11,6 +11,7 @@ My solutions for [Advent of Code](https://adventofcode.com) over the years.
 - [2021](2021-py/): Python
 - [2022](2022-py/): Python / Rust
 - [2023](2023-go/): Golang (all days, < 1000 ms total runtime)
+- [2024](2024-php/): PHP
 
 ## License