Add links to official docs site.

For more details: https://ropensci.org/technotes/2019/06/07/ropensci-docs/

Author: rOpenSci Bot

DESCRIPTION

@@ -5,7 +5,7 @@ Version: 1.8
 Authors@R: person("Chris", "Stubben", role = c("aut", "cre"), email = "[email protected]")
 Description: Parse XML documents from the Open Access subset of Europe PubMed Central <https://europepmc.org>
     including section paragraphs, tables, captions and references.
-URL: https://github.com/ropensci/tidypmc
+URL: https://docs.ropensci.org/tidypmc, https://github.com/ropensci/tidypmc
 BugReports: https://github.com/ropensci/tidypmc/issues
 License: GPL-3
 Encoding: UTF-8