Update reference to external parameter repository

This update adds parameter files corresponding to the trd_v21a geometry for the mCBM beamtine in June 2021.

added 2 commits

• 697e5ddd - 1 commit from branch computing:master
• aff595e4 - Update reference to external parameter repository

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Dear @f.uhlig,

you have been identified as code owner of at least one file which was changed with this merge request.

Please check the changes and approve them or request changes.

added CodeOwners label

merged