Update ISSUE_TEMPLATE.md (microsoft#1293)

* Update ISSUE_TEMPLATE.md

Added a note calling out that this template is only to file issues on vstest CLI.

* addressed PR comments.

.github/ISSUE_TEMPLATE.md

@@ -1,5 +1,7 @@
 ## Description
-> Describe the issue you've observed
+> **IMPORTANT**: if the defect is reproduced only in a workflow from within the Visual Studio IDE then do not report the issue here - instead, please report it using Visual Studio's "Send Feedback" option that can be accessed from the Help menu OR using this link https://developercommunity.visualstudio.com.
+>
+> For a defect reproducable from the vstest command line, describe the issue you've observed.
 
 ## Steps to reproduce
 > What steps can reproduce the defect?