Create a .github README for github.com/MariaDB

Following a discussion, with @Otto Kekäläinen and others from AWS, they suggested a .github repo to make the landing page for MariaDB on GitHub more appealing.

Here is an example:
https://github.com/langchain-ai/.github
And here is how it looks:
https://github.com/langchain-ai

We should set up something similar for MariaDB organization on Github.