Add ISSUE_TEMPLATE file for github issue templates

Add the ISSUE_TEMPLATE file which is what github uses for providing the
default text on the new issue page

Closes coala#2735

ISSUE_TEMPLATE

@@ -0,0 +1,6 @@
+<!-- Hello! If you're filing a bug, please include every step so as to help us reproduce it on our machines. If you're unsure about how to file an issue, use the issue template. If you need any help regarding usage of coala, check out the documentation or hit us up on chat. You can ignore or delete this text, it is commented and won't appear when the issue is submitted or previewed.
+
+Chat: https://coala.io/chat
+Issue Template: https://github.com/coala/coala/blob/master/CONTRIBUTING.rst#filing-issues
+Documentation: https://docs.coala.io
+-->