Update SECURITY.md

I'd like to report a security issue and felt it most prudent not to disclose it publicly, as per your Security policy instructions.

If not a hassle, might you kindly add an email, or other private contact method? GitHub [recommends](https://docs.github.com/en/code-security/getting-started/adding-a-security-policy-to-your-repository) this best practice to ensure security issues are responsibly disclosed, and it would serve as a simple instruction for security researchers in the future.

Thank you for your consideration!

SECURITY.md

@@ -10,5 +10,6 @@ currently being supported with security updates.
 | 1.x.x  | :white_check_mark: |
 
 ## Reporting a Vulnerability
+Please report security issues to <email>
 
 https://github.com/louislam/uptime-kuma/issues