docs(emacs, fish): add eww-related features

Emacs: add yuck-mode with parinfer-rust-mode enabled by default.

Fish: add eww autocompletions

docs/fish.org

@@ -40,6 +40,11 @@ for fish.
 direnv hook fish | source
 #+end_src
 
+I also use [[https://github.com/elkowar/eww/][eww]] for some widgets, let’s load its shell completions.
+#+begin_src fish
+eww shell-completions --shell fish | source
+#+end_src
+
 Since I don’t really have a better place on this website to put it,
 here is my direnv configuration located at
 =$HOME/.config/direnv/direnv.toml=.