Add docs clarifying compatibility with MariaDB

[robinnewhouse]

Peewee is compatible with MariaDB Server. Add clarifying notes in the documentation, including logo, etc.

Testing

docker run -d -p 3306:3306 --name mariadb_container -e MYSQL_ROOT_PASSWORD=password mariadb

>>> from peewee import MySQLDatabase
>>> database = MySQLDatabase('information_schema', user='root', password='password', host='127.0.0.1', port=3306)
>>> database.connect()
True
>>> version_query = database.execute_sql('SELECT VERSION()')
>>> print(version_query.fetchone()[0])
11.3.2-MariaDB-1:11.3.2+maria~ubu2204
>>> database.close()
True

[coleifer]

We don't explicitly mention this because it should already be quite obvious to anyone who uses MariaDB. They speak the same wire protocol and use the same client libraries, so I don't think anything special is needed here.

[coleifer]

Eh, what the heck, I'll just clean it up a bit. Thanks.