[readme] fish: send output from load_nvm to /dev/stderr

Author: PonderCodes

README.md

@@ -666,7 +666,7 @@ end
 
 # ~/.config/fish/config.fish
 # You must call it on initialization or listening to directory switching won't work
-load_nvm
+load_nvm > /dev/stderr
 ```
 
 ## Running Tests