update doc

README.md

@@ -95,10 +95,6 @@ z -b foo    # cd to the parent directory starting with foo
 
   This is another way to initialize z.lua in fish shell, but remember to regenerate z.fish if z.lua has been updated or moved.
 
-  Package managers like oh-my-fish are currently supported, you can install z.lua from url: 
-
-      omf install https://github.com/skywind3000/z.lua
-
 - Power Shell:
 
   put something like this in your `profile.ps1`: