Document second method of adding quitcd to fish

scripts/quitcd/quitcd.fish

@@ -1,5 +1,6 @@
 # Rename this file to match the name of the function
 # e.g. ~/.config/fish/functions/n.fish
+# or, add the lines to the 'config.fish' file.
 
 export NNN_TMPFILE="/tmp/nnn"