As @mishabalyasin says, you are using the development version of dplyr, which I am guessing you installed via:
devtools::install_github("tidyverse/dplyr")
Unlike install.packages() (which installs the stable version from CRAN), devtools::install_github() does not build the package vignettes by default. To get them, you should do:
devtools::install_github("tidyverse/dplyr", build_vignettes = TRUE)
After that, you should be able to call the vignette after loading the package:
library(dplyr)
vignette("colwise")