Add SECURITY.md

Author: errfrom

SECURITY.md

@@ -0,0 +1,17 @@
+# Security Policy
+
+## Reporting a Vulnerability
+
+Please report any (suspected) security vulnerabilities to info@mlabs.city.
+If the issue is confirmed, we will release a patch as soon as possible.
+
+Please provide a clear and concise description of the vulnerability, including:
+
+* the affected version(s) of cardano-transaction-lib,
+* steps that can be followed to exercise the vulnerability,
+* any workarounds or mitigations
+
+If you have developed any code or utilities that can help demonstrate the
+suspected vulnerability, please mention them in your email but ***DO NOT***
+attempt to include them as attachments as this may cause your Email to be
+blocked by spam filters.