Add link to directive to mda8 documentation

[thorbjoernl]

Change Summary

Small PR to add a link to the mda8 EU directive to the documentation for mda8

Related issue number

NA

Checklist

• Start with a draft-PR
• The PR title is a good summary of the changes
• PR is set to AeroTools and a tentative milestone
• Documentation reflects the changes where applicable
• Tests for the changes exist where applicable
• Tests pass locally
• Tests pass on CI
• At least 1 reviewer is selected
• Make PR ready to review

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.96%. Comparing base (9e48af9) to head (71152cc).
Report is 385 commits behind head on main-dev.

Additional details and impacted files

@@             Coverage Diff              @@
##           main-dev    #1318      +/-   ##
============================================
- Coverage     78.97%   78.96%   -0.01%     
============================================
  Files           136      136              
  Lines         20812    20813       +1     
============================================
  Hits          16436    16436              
- Misses         4376     4377       +1     

Flag	Coverage Δ
unittests	78.96% <ø> (-0.01%)	⬇️

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