Improve docs around new_edits=true/false to mention conflicts

In https://developer.couchbase.com/documentation/mobile/current/references/sync-gateway/rest-api/index.html?v=2.0#/database/post__db___bulk_docs it shows 

I think it might be worth it to expand on that and mention the behavior around conflicts.  For example mention that Couchbase Lite typically uses new_edits=false so that it can create conflicting revs if needed.  And that if you wanted to avoid creating conflicts, you would want to use new_edits=true.  "Indicates whether to assign new revision identifiers to new edits." doesn't mean a lot to me.

Related to https://github.com/couchbase/sync_gateway/issues/3518 .. I'm planning to link to the docs to try to explain to the user how to correctly use the API.