Expand `@includeRmd` in the description section

[lionel-]

From @gaborcsardi: We can't have nested roxygen tags currently, but the section to expand to could be a parameter.

[gaborcsardi]

#' @includeRmd description path/to/file.Rmd

might work. Somewhat ambiguous, but that's probably OK.

[hadley]

Doesn't this work already?

https://github.com/r-lib/tidyselect/blob/master/R/faq.R#L1-L7

yields

https://github.com/r-lib/tidyselect/blob/master/man/faq-external-vector.Rd#L7

[gaborcsardi]

@hadley: that's only because the Rmd starts with a ##, which creates a subsection. If you start with # or with just non-heading text, that'll go into @details I think.

[lionel-]

@hadley I hardcoded description in my local roxygen.