Use R Notebooks for development. Notebooks are self contained and can be emailed as a single document, like a MS Word file.
File > New File > R Notebook
Use HTML documents for more fixed content. HTML Documents will cache better and potentially load faster.
File > New File > R Markdown... > Document > HTML
R Markdown: The Definitive Guide book by Yihui Xie, J. J. Allaire, Garrett Grolemund