Switch install.sh to GNU Stow for symlinking

Manual ln -sfn loop replaced with stow zsh gnupg, matching the repo's
existing per-package-directory convention. Still backs up/removes any
conflicting file or foreign symlink at the target before stowing.

README.md

@@ -5,15 +5,21 @@ My configuration files that keep me from flipping a table after logging in.
 ## Setup
 
 ```
+sudo pacman -S stow   # or your distro's equivalent
 git clone https://github.com/andwati/dotfiles ~/dev/dotfiles
 ~/dev/dotfiles/install.sh
 ```
 
-Symlinks `zsh/.zshrc`, `zsh/.zshenv`, `zsh/.zprofile`, `zsh/.p10k.zsh`, and
-`gnupg/.gnupg/gpg-agent.conf` into `$HOME`, and clones oh-my-zsh plus the
-theme/plugins `.zshrc` expects (powerlevel10k, zsh-autosuggestions,
-zsh-syntax-highlighting, zsh-history-substring-search, zsh-completions,
-you-should-use).
+Each top-level directory is a [GNU Stow](https://www.gnu.org/software/stow/)
+package mirroring `$HOME` (e.g. `zsh/.zshrc` -> `~/.zshrc`). `install.sh`
+clones oh-my-zsh plus the theme/plugins `.zshrc` expects (powerlevel10k,
+zsh-autosuggestions, zsh-syntax-highlighting, zsh-history-substring-search,
+zsh-completions, you-should-use), then runs `stow zsh gnupg` to link
+everything in, backing up any conflicting real files it finds first (e.g.
+oh-my-zsh's own freshly-installed `.zshrc`).
+
+To add a new package: create a top-level dir shaped like `$HOME` (e.g.
+`git/.gitconfig`), then add a `stow_package <name>` call in `install.sh`.
 
 `gpg-agent.conf` caches your GPG passphrase for 8 hours (24h hard cap)
 instead of the 10-minute default, so signed commits don't re-prompt