Add a basic SECURITY.md that points to support.fauna.com (#534)

* Add a basic SECURITY.md that points to support.fauna.com

* Clean up supported versions

* Point users to trust.fauna.com

SECURITY.md

@@ -0,0 +1,19 @@
+# Security Policy
+
+## Supported Versions
+
+Use this section to tell people about which versions of your project are
+currently being supported with security updates.
+
+| Version | Supported          |
+| ------- | ------------------ |
+| 4.x.x   | :white_check_mark: |
+| < 4.0.0 | :white_check_mark: |
+
+## Reporting a Vulnerability
+
+We believe our user community and unaffiliated security researchers play an important role in
+helping to keep Fauna and our customers secure. If you think you have found a security issue,
+please inform us by sending an email to [email protected].
+
+Learn more about reporting a vulnerability at [trust.fauna.com](https://trust.fauna.com/).