fix link to gt article

Author: mrcaseb

vignettes/articles/nflplotR.Rmd

@@ -445,7 +445,7 @@ ggplot(mtcars, aes(x = mpg, y = disp)) +
 
 # nflplotR and the gt package
 
-See `vignette("gt")`.
+Please see the [separate "gt" article](https://nflplotr.nflverse.com/articles/gt.html).
 
 # How about speed in the RStudio preview pane?