tmuxinator: add README (#7189)

plugins/tmuxinator/README.md

+# Tmuxinator plugin
+
+This plugin provides completion for [tmuxinator](https://github.com/tmuxinator/tmuxinator),
+as well as aliases for frequent tmuxinator commands.
+
+To use it add `tmuxinator` to the plugins array in your zshrc file.
+
+```zsh
+plugins=(... tmuxinator)
+```
+
+## Aliases
+
+| Alias  | Command          | Description              |
+| ------ | ---------------- | ------------------------ |
+| `txs ` | tmuxinator start | Start Tmuxinator         |
+| `txo ` | tmuxinator open  | Open project for editing |
+| `txn ` | tmuxinator new   | Create project           |
+| `txl ` | tmuxinator list  | List projects            |