Add example config for using standalone syntax with vimwiki (#341)

Co-authored-by: Caleb Maclennan <caleb@alerque.com>

Author: Ashish Panigrahi

README.md

@@ -40,6 +40,15 @@ Vim to load it for certain files. Just add something like this to your vimrc:
     augroup END
 ~~~
 
+For vimwiki users, use
+
+~~~ vim
+augroup pandoc_syntax
+  autocmd! FileType vimwiki set syntax=markdown.pandoc
+augroup END
+~~~
+
+
 ## Features
 
 * Supports most (if not all) pandoc's markdown features, including tables,