add existing dir warning and how to fix it

Author: ocefpaf

resources/prep/jupyterhub.md

@@ -50,7 +50,9 @@ You can accomplish the same results as nbgitpuller when using `git` directly, bu
 
 ```{warning}
 
-If you start by using the nbgitpuller link, and then switch to using git directly, using the nbgitpuller link again will most likely lead to [unpredictable results](https://jupyterhub.github.io/nbgitpuller/#when-to-use-nbgitpuller).
+If you start by using the nbgitpuller link, and then switch to using git directly, or if you already have a copy of the repository in our account, using the nbgitpuller link again will most likely lead to [unpredictable results](https://jupyterhub.github.io/nbgitpuller/#when-to-use-nbgitpuller).
+
+This can be fixed by [removing the `ohw-tutorials` directory](https://imgs.xkcd.com/comics/git.png) and using nbgitpuller again.
 ```