chore: add AI usage disclaimer for Slack docs (#398)

- Slack marketplace guidelines expect us to add disclaimer on AI usage on
our landing page

Author: Prashant-Surya

docs/integrations/slack.mdx

@@ -206,6 +206,10 @@ This keeps you updated on work that requires your attention without checking Pla
 
 Interact with Plane AI directly from Slack to create work items, check project status, and get updates—all through natural conversation.
 
+:::info[Disclaimer]
+Plane uses AI models powered by Anthropic. AI-generated responses may not always be accurate.
+:::
+
 #### Mention @Plane in threads
 
 Tag `@Plane` in any Slack thread to ask questions or request actions: