add protocolhelper package

[hansvancalster]

This PR addresses #183 partly (action still needed from other package maintainers).

Note, when I tried to preview the md file, the following error appeared:

"C:/Users/HANS_V~1/AppData/Local/Pandoc/pandoc" +RTS -K512m -RTS index.utf8.md --to gfm --from markdown+autolink_bare_uris+tex_math_single_backslash --output index.md --standalone --filter "C:/Users/HANS_V~1/AppData/Local/Pandoc/pandoc-citeproc.exe" 
pandoc-citeproc.exe: PandocResourceNotFound "download.file(\8220https://github.com/citation-style-language/styles/raw/master/research-institute-for-nature-and-forest.csl\8221, tempfile())"
Error running filter C:/Users/HANS_V~1/AppData/Local/Pandoc/pandoc-citeproc.exe:
Filter returned error status 1
Error: pandoc document conversion failed with error 83
Execution halted

but I don't see any problems or changes I made in the md file that might cause this error. So I think it should be OK.

[florisvdh]

Fine contribution @hansvancalster. One suggestion to keep the table consistent.

I'll drop the csl and biblio keys here, it is junk I erroneously included in this article it seems (#202). The md files are not meant for knitting in R anyway; for this article we chose to drop the Rmd file and just write plain markdown.