Update README for fish completion

etc/README.md

@@ -35,3 +35,12 @@ Then add the following lines to your `.zshrc` file:
 fpath=(~/.zsh/completions $fpath) 
 autoload -U compinit && compinit
 ```
+
+## fish
+
+Copy the file `/etc/hub.fish_completion` from the location where you downloaded `hub` to the folder `~/.config/fish/completions/` and rename it to `hub.fish`:
+
+```sh
+cp /path/to/etc/hub.fish_completion ~/.config/fish/completions/
+mv ~/.config/fish/completions/hub.fish_completion ~/.config/fish/completions/hub.fish
+```