docs: adicionando MAINTAINING.md

[camilamaia]

Closes #425

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.78%. Comparing base (3549669) to head (04f30ea).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #427   +/-   ##
=======================================
  Coverage   99.78%   99.78%           
=======================================
  Files          18       18           
  Lines         472      472           
=======================================
  Hits          471      471           
  Misses          1        1           

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