add MariaDB to README and doc

[robertsilen]

Suggest to add MariaDB to README and documentation intro as mentioned in #719 - hope this is ok?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.86%. Comparing base (e2a908b) to head (5e2843a).
Report is 23 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #720   +/-   ##
=======================================
  Coverage   88.86%   88.86%           
=======================================
  Files           7        7           
  Lines         548      548           
=======================================
  Hits          487      487           
  Misses         61       61           

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