Docs: Staging info may be incomplete

[robb-romans]

@edwardjrp
Basically how the content presentation happens when you publish the same content compiled with different content id base ID, thats what the revisions for staging do, but the way it shows those multiple revs is kind of a trick that presenter does to identify the content, which it works but you have to enable something called STAGING_MODE in presenter, i found out about that going through the code, that particular variable and behavior is mentioned in the staging env explanation but nothing said about presenter needing that mode to be on.

https://github.com/deconst/presenter/blob/master/src/config.js#L89

https://github.com/deconst/deconst-docs/blob/master/developing/staging.rst#submitting-content-to-the-staging-environment