doc: add readme to zsh

roles/zsh/README.md

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+# zsh configuration
+
+## Features
+
+- **Powerlevel10k** theme with instant prompt
+- **Syntax highlighting** for commands
+- **Autosuggestions** based on history
+- **fzf integration** (Ctrl+R history, Ctrl+T files, Alt+C directories)
+- **fzf-tab** for completion menus
+- **Smart aliases** (docker → podman)
+- **Persistent history** across sessions
+
+## Configuration
+
+### Users
+
+Configure users in inventory:
+
+```yaml
+zsh_users:
+  - jsmith
+  - root
+```
+
+## Keybindings
+
+- `↑/↓` - History search with substring matching
+- `Ctrl+R` - Fuzzy history search
+- `Ctrl+T` - Fuzzy file search
+- `Alt+C` - Fuzzy directory change
+- `Tab` - fzf completion menu