Improve Autocompletion Setup Instructions

[grant]

Expected Behavior

There should be very clear instructions on how to provide autocompletion for workflow files. And an image/GIF.

[rogerthatdev]

I've added this issue as a feature request for future consideration.

[meteatamel]

FYI, I blogged about this a while back, in case it's useful: https://medium.com/google-cloud/auto-completion-for-workflows-json-and-yaml-on-visual-studio-code-875a5e878d5e