update moderation docs (#10002)

docs/docs_skeleton/docs/guides/safety/index.mdx

@@ -1,6 +1,7 @@
-# Preventing harmful outputs
+# Moderation
 
 One of the key concerns with using LLMs is that they may generate harmful or unethical text. This is an area of active research in the field. Here we present some built-in chains inspired by this research, which are intended to make the outputs of LLMs safer.
 
 - [Moderation chain](/docs/guides/safety/moderation): Explicitly check if any output text is harmful and flag it.
 - [Constitutional chain](/docs/guides/safety/constitutional_chain): Prompt the model with a set of principles which should guide it's behavior.
+- [Amazon Comprehend moderation chain](/docs/guides/safety/amazon_comprehend_chain): Use [Amazon Comprehend](https://aws.amazon.com/comprehend/) to detect and handle PII and toxicity.