Add SECURITY.md (#846)

Copied and adjusted from:

  * https://github.com/dotnet/runtime/blob/b443b8ccce174ef0e87183e21561c4ff13373cfd/SECURITY.md

Author: jpobst

SECURITY.md

@@ -0,0 +1,15 @@
+# Security Policy
+
+Java.Interop is supported as a component of Xamarin.Android.
+
+## Supported Versions
+
+The Xamarin.Android support policy, including supported versions, can be found at the [Xamarin Support Policy](https://dotnet.microsoft.com/platform/support/policy/xamarin).
+
+## Reporting a Vulnerability
+
+Security issues and bugs should be reported privately to the Microsoft Security Response Center (MSRC), either by emailing secure@microsoft.com or via the portal at https://msrc.microsoft.com.
+You should receive a response within 24 hours. If for some reason you do not, please follow up via email to ensure we received your
+original message. Further information, including the MSRC PGP key, can be found in the [MSRC Report an Issue FAQ](https://www.microsoft.com/en-us/msrc/faqs-report-an-issue).
+
+Please do not open issues for anything you think might have a security implication.