Add autocomplete example

[coolaj86]

It looks like vim-ale supports autocomplete.

I'd be interested to see what that could look like.

Could probably prototype with vscode-language-server (but it seems like it's wicked slow, so maybe not production?).

let g:ale_completion_enabled = 1
let g:ale_lsp_suggestions = 1

~/.vim/pack/plugins/start/ale/
    doc/ale-supported-languages-and-tools.txt
    autoload/ale/completion.vim
    autoload/ale/lsp.vim
    plugin/ale.vim