add Hugo documentation

[xenophenes]

IMPORTANT

The docs directory now contains the published version of the Hugo website.

The hugo directory now contains the developer's version of the Hugo website.

When editing documentation, navigate to $COROOT/hugo/content and modify the documents accordingly. $COROOT/hugo/content/_index.adoc is the equivalent of README.adoc. All other documents are edited in a logical fashion.

If when writing new documentation, you want to use shortcodes (for example, what's shown on the Upgrading the Operator page - the drop downs), visit this link: http://docdock.netlify.com/shortcodes/

When ready to publish changes to documentation, the workflow is as follows:

cd $COROOT/hugo/
hugo
git add --all && git commit
git push

That simple! When the hugo command is run, it publishes the generated version of the website in the $COROOT/docs directory.

The site should be accessible from crunchydata.github.io/postgres-operator after you navigate to https://github.com/crunchydata/postgres-operator/settings and select "Source -> master branch /docs folder".

For a working demo of the website, visit https://xenophenes.github.io/pgo-docs/