Add kitty.conf to dotfiles and set as default terminal

- Add .config/kitty/kitty.conf
- setup.sh now sets kitty as default terminal via update-alternatives
- README updated to include kitty.conf

setup.sh

@@ -23,6 +23,9 @@ echo ">>> Installing bash, kitty, and vim..."
 sudo apt update
 sudo apt install -y bash kitty vim-gtk3 git curl
 
+echo ">>> Setting kitty as default terminal..."
+sudo update-alternatives --install /usr/bin/x-terminal-emulator x-terminal-emulator /usr/bin/kitty 20
+
 # 2. Clone your dotfiles (bare repo style)
 if [ ! -d "$HOME/.dotfiles" ]; then
     echo ">>> Cloning dotfiles repo..."