Create ISSUE_TEMPLATE

Author: jtattermusch

.github/ISSUE_TEMPLATE

@@ -0,0 +1,14 @@
+Please answer these questions before submitting your issue.
+
+### What version of gRPC are you using?
+
+### What version of Go are you using (`go version`)?
+
+### What operating system (Linux, Windows, …) and version?
+
+### What did you do?
+If possible, provide a recipe for reproducing the error.
+
+### What did you expect to see?
+
+### What did you see instead?