Repository address in the format
username/repo[/subdir][@ref|#pull]. Alternatively, you can
specify subdir and/or ref using the respective parameters
(see below); if both is specified, the values in repo
ref
Desired git reference. Could be a commit, tag, or branch
name, or a call to github_pull. Defaults to "master".
subdir
subdirectory within repo that contains the R package.