Re-added proper frontmatter to markdown template

I'd removed the hashmarks from the markdown frontmatte tempplate so I
could use tags in SilverBullet, but decided against using SilverBullet
regularly. Not enough to break proper formatting.

.vim/templates/mdfm

@@ -1,6 +1,9 @@
 :insert
+---
 filename:
 filecreated:
 fileupdated: 
 filetags: 
+---
+