Fixed tntpr installation instructions in the visualization cookbook.

vignettes/visualization-cookbook.Rmd

@@ -24,13 +24,10 @@ We'll get to how you can put together the various elements of these graphics, bu
 
 ## Install the `tntpr` package
 
-`tntpr` is not on CRAN, so you will have to install it directly from Github using `devtools`.
-
-If you do not have the `devtools` package installed, you will have to run the first line in the code below as well. This command will also work for updating `tntpr` if you already have it installed.
+You can install `tntpr` from CRAN as follows:
 
 ```{r eval=FALSE}
-# install.packages('devtools')
-devtools::install_github('tntp/tntpr')
+install.packages('tntpr')
 ```
 
 ## Load all the libraries you need