A table of contents would help the reader to go through the document. Furthermore, some sections should be added:

• It would be helpful to have a FAQ section in the readme, also known as troubleshooting.

• There should be a team section where everyone is acknowledged.

Also have a look into the vignettes, which is used for teaching aspects in R packages:
http://r-pkgs.had.co.nz/vignettes.html