Deflect some issues which are not bugs

I think we should make it more clear that connection issues are generally not bugs and should be sent to the mailing list or IRC etc.

What do you think?

.github/ISSUE_TEMPLATE.md

@@ -1,8 +1,13 @@
+_Read these instructions before submitting_
+
 **DELETE THIS TEMPLATE BEFORE SUBMITTING**
 
 _Only use Github issues to report bugs or feature requests, see
 https://www.packer.io/community.html_
 
+Specifically we _don't accept_ issues for:
+- _Timeout waiting for SSH/WinRM_ - Unless there is evidence pointing towards a bug in packer. e.g it works with a previous version, or you can manually connect with the same credentials, etc. Ask on the mailing list if you are unsure.
+
 If you are planning to open a pull-request just open the pull-request instead of making an issue first.
 
 FOR FEATURES: