Update rd.Rmd

I believe this is just a typo, `@value` is not the tag for returning `@return` is (though I have always found this confusing as the Rd file section associated with `@return` is actually called `"Value"`; it might be worth changing `@return` to `@value`).
Merge pull request #192 from dougmitarotonda/patch-1

Update rd.Rmd