Add custom completions for aws-cli

[Yethal]

Aws-cli ships with a dedicated completion binary that only needs to be passed current commandline to work. Space is appended to returned results so that completing subcommands can be done simply by pressing tab multiple times

[fdncred]

I don't think the aws folder exists yet. Do you mind adding a readme.md to that folder explaining what this is for and where to get it? It's kind of our custom to explain this stuff for people who aren't aware.

[Yethal]

Done

[fdncred]

Thanks @Yethal. Appreciate your support!