Position your cursor at the end of the first sentence (right after the period) and then click Cite. You can automatically add the journal article citation with either the URL — http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0184311 — or the DOI — 10.1371/journal.pone.0184311. (If it was a book, you could use the ISBN.)
Once you've inserted the citation, publish the changes.