zk: Add a horizontal ruler before the modeline

When using the zettel as a commit message this is also convenient as git
will ignore everything behind it. (Which also means that all horizontal
rulers in a zettel should use atleast 4 dashes)

.config/zsh/autoload/zk

@@ -24,10 +24,13 @@ dir="$(date +"%Y/%m/%d/%H%M%S")"
 mkdir -p "$dir"
 
 if [[ ! -e "$dir/README.md" ]]; then
-	# Paste zettel template
+	# Paste zettel template, including header prefix, end-of-payload divider and
+	# vim-modeline
 	cat >"$dir/README.md" <<-EOF
 	# 
 
+	---
+
 	<!--- vim: set ft=markdown.zettel: -->
 	EOF
 else