When you create a new plumber file from the RStudio IDE menu, you get the following:
library(plumber)
#* @apiTitle Plumber Example API
This already provides you with the template for modifying the API title. You can then add the API description in a similar way, and add the API version while your'e at it:
library(plumber)
#* @apiTitle Your title goes here
#* @apiDescription Your description goes here
#* @apiVersion 0.0.1.9000
Your swagger page should look like this: