[8.17] Adds legend to LLM perf matrix (backport #6297) (#6322)

* adds note to LLM perf matrix (#6297)

(cherry picked from commit a74bc31)

# Conflicts:
#	docs/serverless/AI-for-security/llm-performance-matrix.asciidoc

* Delete docs/serverless directory and its contents

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Co-authored-by: Benjamin Ironside Goldstein <[email protected]>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: 3 people

docs/AI-for-security/llm-performance-matrix.asciidoc

@@ -13,4 +13,5 @@ This table describes the performance of various large language models (LLMs) for
 | *Assistant - Knowledge retrieval* | Good        |  Excellent              | Excellent            | Excellent          | Excellent         | Excellent | Great         | Excellent           | Excellent
 | *Attack Discovery*            | Great           |  Great                  | Excellent            | Poor               | Poor              | Great     | Poor          | Excellent           | Poor 
 |===
- 
+ 
+NOTE: `Excellent` is the best rating, followed by `Great`, then by `Good`, and finally by `Poor`.