Add vimwiki to neovim and change wiki syntax

[n-murphy]

Add the following to the init.vim

set nocompatible
filetype plugin on
syntax on
call plug#begin()
Plug 'vimwiki/vimwiki'
call plug#end()
let g:vimwiki_list = [{'path': '/path/to/my/wiki/',
                      \ 'syntax': 'markdown', 'ext': '.md'}]