Update ISSUE_TEMPLATE.md

[ci skip]

ISSUE_TEMPLATE.md

@@ -1,9 +1,15 @@
 - Neovim version:
-- Operating system:
-- Terminal emulator:
+- [ ] Vim behaves differently?
+    - Vim version:
+- Operating system/version:
+- Terminal name/version:
+- `$TERM`:
 
 ### Actual behaviour
 
 ### Expected behaviour
 
-### Steps to reproduce
+### Steps to reproduce using `nvim -u NONE`
+
+1. `nvim -u NONE`
+2.