Docs: mention MariaDB in README (CI already tests MariaDB)

[robertsilen]

Hi — I was looking at compatibility for MariaDB users and noticed your GitHub Actions workflow (.github/workflows/ci.yml) runs integration tests against MariaDB 5.5 through 10.4, in addition to MySQL.

The README’s “Running integration tests” section only refers to a MySQL server, so it’s easy to miss that MariaDB is already exercised in CI.

Would you be open to a small documentation PR? I’d suggest:

1. In Introduction — one sentence that the driver targets the MySQL protocol and is routinely tested against MariaDB (as well as MySQL).
2. In Running integration tests — note that the project’s CI matrix includes MariaDB versions (and that local testing can use any MySQL-protocol-compatible server, including MariaDB).

Happy to open a PR if that sounds reasonable?