Update gao_iet.md

Add description and no mechanism #221 (closed)

added DefenseSystem label

requested review from @hgeorjon

assigned to @ftesson

added 73 commits

• 2f6d62b6...9fd810f9 - 71 commits from branch main
• da7ee98f - Merge branch 'main' into ftesson_gao_iet
• f2aba847 - merge main correct misspelling

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merged

mentioned in commit d8bcddd5