chore: add guidelines w.r.t. valid security issues (#1829)

Author: mathiasbynens

SECURITY.md

@@ -1,3 +1,9 @@
 ## Security policy
 
 The Chrome DevTools MCP project takes security very seriously. Please use [Chromium’s process to report security issues](https://www.chromium.org/Home/chromium-security/reporting-security-bugs/).
+
+### Scope
+
+In general, it is the expectation that the AI agent or client using this MCP server validates any input before sending it. The server provides powerful capabilities for browser automation and inspection, and it is the responsibility of the calling agent to ensure these are used safely and as intended.
+
+Several tools in this project have the ability to perform actions such as writing files to disk (e.g., via browser downloads or screenshots) or dynamically loading Chrome extensions. These are intentional, documented features and are not vulnerabilities.