docs: add Security Policy doc (paritytech#1770)

Signed-off-by: acatangiu <adrian@parity.io>

bridges/SECURITY.md

@@ -0,0 +1,14 @@
+# Security Policy
+
+Thanks for helping make the Parity ecosystem more secure. Security is one of our first priorities.
+
+## Reporting a vulnerability
+
+If you find something that can be treated as a security vulnerability, please do not use the issue tracker or discuss it in the public forum as it can cause more damage, rather than giving real help to the ecosystem.
+
+Security vulnerabilities should be reported by the [contact form](https://security-submission.parity.io/).
+
+If you think that your report might be eligible for the Bug Bounty Program, please mark this during the submission. Please check up-to-date [Parity Bug Bounty Program rules](https://www.parity.io/bug-bounty) to find out the information about our Bug Bounty Program.
+
+**Warning**: This is an unified SECURITY.md file for Paritytech GitHub Organization. The presence of this file does not mean that this repository is covered by the Bug Bounty program. Please always check the Bug Bounty Program scope for information.
+