Add issue template

.github/ISSUE_TEMPLATE.md

+<!--
+  Problem with the demonstration server? 
+    -> Please retry in a few hours or send me directly an email: https://github.com/Chocobozzz
+  Bug?
+    -> Please check first you're running on the latest version of Firefox/Chromium
+    -> Please check the console log to add informations to the bug report
+-->
+
+* Browser name/version:
+* Console log if useful (Gist/Pastebin...):