Adds autocommand for updating the shared file

This allows neovim instances to share registers, marks, command history
and some other bits.

See :h shada

Augroup stolen from here:

https://vi.stackexchange.com/a/24564

nvim/.config/nvim/plugin/settings.vim

@@ -64,3 +64,10 @@ augroup colorcols
 	autocmd!
 	autocmd FileType,VimEnter,BufEnter * call mine#functions#colorcols()
 augroup end
+
+" share data between nvim instances (registers etc)
+augroup SHADA
+	autocmd!
+	autocmd CursorHold,TextYankPost,FocusGained,FocusLost *
+		\ if exists(':rshada') | rshada | wshada | endif
+augroup END