Make automatic installation script in wiki tips compatible with Neovim

When using the snippet to auto install everything on Neovim it does not recognise `PlugInstall` as a command without restarting.
To solve this I added one line to the suggested tip to source Plug right after downloading it.

It now looks as follows (in lua):
```
local data_dir = fn.stdpath('data')
if vim.fn.empty(vim.fn.glob(data_dir .. '/site/autoload/plug.vim')) == 1 then
vim.cmd('silent !curl -fLo ' ..
data_dir ..
'/site/autoload/plug.vim --create-dirs https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim')
vim.cmd('source ' .. data_dir .. '/site/autoload/plug.vim')
vim.cmd('autocmd VimEnter * PlugInstall --sync | source $MYVIMRC')
end
```

Would it be possible to add this solution for those who get the error that `PlugInstall` is not a command on first setup with this tip?

```
NVIM v0.9.5
Build type: Release
LuaJIT 2.1.1703358377
```

- Type:
- [ ] Bug
- [x] Enhancement
- [ ] Feature Request
- [ ] Question
- OS:
- [x] All/Other
- [ ] Linux
- [ ] macOS
- [ ] Windows
- Vim:
- [ ] Terminal Vim
- [ ] GVim
- [x] Neovim