Fixed zsh instruction in README

README.md

@@ -96,11 +96,13 @@ end
 ```  
 
 ### `zsh`  
-Export the `PS1` variable with the output of `prettyprompt $?` as its value.  
+Use the precmd function to set the `PROMPT` variable with the output of `prettyprompt $?` as its value.  
 User-specific: `~/.zshrc`  
 System-wide: `/etc/zsh/zshrc`  
-```sh    
-export PS1="$(prettyprompt $?)" # Notice the double quotes
+```zsh  
+precmd() {  
+    PROMPT="$(prettyprompt $?)" # Notice the double quotes  
+}  
 ```  
 
 ### Other shells