Add Docker Compose example and MySQL data persistence

[NecroPrism4]

I needed to run this docker image whit docker compose particularly, also I needed data persistent with mysql.

• Added a Docker Compose example to the README.md file demonstrating how to mount a volume in the MySQL directory for data persistence.

This example is usefull if you needto run the tomsik68/xampp Docker image with Docker Compose and you require ensuring data persistence for MySQL. However, attempting to mount a volume directly to the MySQL directory may lead to errors during boot up. This PR addresses this issue by providing a clear example and instructions on how to correctly configure Docker Compose for MySQL data persistence.

[tomsik68]

LGTM. Thank you for the contribution!