[llvm] Add llvm-project archive issues for Chromium bug tracker (PR #132030)

[Peter Smith via llvm-commits]

================
@@ -2,7 +2,15 @@
 LLVM Security Group Transparency Reports
 ========================================
 
-This page lists the yearly LLVM Security group transparency reports.
+This page lists the yearly LLVM Security Response group transparency reports.
+
+The LLVM Security Response group started out as the LLVM security group, previous
+year's transparency reports keep the original year.
+
+Initially the Chromium issue tracker was used to record issues. This component
+has been archived and is read-only. A llvm-project issue with the SecurityArchive
+label has been created with a further backup PDF copy in a llvm-project
+repository.
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smithp35 wrote:

I've adopted something closer to Kristof's text, hopefully a bit easier to read now.

https://github.com/llvm/llvm-project/pull/132030