Add security disclosure note to README

Adds a short note explaining how to report security issues responsibly.

Author: ManyChavez

README.md

@@ -143,3 +143,9 @@ For support please join our [Discord](https://discord.gg/buildonbase) post in `
 THE NODE SOFTWARE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. We make no guarantees about asset protection or security. Usage is subject to applicable laws and regulations.
 
 For more information, visit [docs.base.org](https://docs.base.org/).
+
+## Security
+
+If you discover a security issue, please do not open a public issue.
+Instead, follow the responsible disclosure process described by the Base team.
+