a high-level description of the package and its goals
R code to install from GitHub, if GitHub usage detected
a basic example
Use Rmd if you want a rich intermingling of code and data. Use
md for a basic README. README.Rmd will be automatically
added to .Rbuildignore. The resulting README is populated with default
YAML frontmatter and R fenced code blocks (md) or chunks (Rmd).