added new issue template

Author: jaymedavis

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,5 @@
+Please only file issues here that you believe represent actual bugs or feature requests for the Stripe.net library.
+
+If you're having general trouble with your Stripe integration, please reach out to Stripe support using the form at https://support.stripe.com/ (preferred) or via email to support@stripe.com.
+
+If you are reporting a bug, please include your OS version, .NET version and the version of the Stripe.net library you're using, as well as any other details that may be helpful in reproducing the problem.