Add documentation comments to benchmark workflow

Co-authored-by: hsluoyz <3787410+hsluoyz@users.noreply.github.com>

Author: Copilot

.github/workflows/benchmark.yml

@@ -1,3 +1,18 @@
+# Performance Benchmark CI Workflow
+#
+# This workflow automatically runs performance benchmarks on pull requests
+# and posts a comparison comment showing speed differences between the PR
+# and the base branch (master).
+#
+# The workflow:
+# 1. Runs benchmarks on the PR branch
+# 2. Runs benchmarks on the base branch (master)
+# 3. Compares the results and identifies performance regressions/improvements
+# 4. Posts a detailed comparison table as a PR comment
+#
+# Performance changes > 10% are flagged as significant to help maintainers
+# catch performance regressions before merging.
+
 name: Performance Benchmark
 
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