rsync: add README (#7188)

plugins/rsync/README.md

+# rsync
+
+This plugin adds aliases for frequent [rsync](https://rsync.samba.org/) commands.
+
+To use it add `rsync` to the plugins array in you zshrc file.
+
+```zsh
+plugins=(... rsync)
+```
+
+| Alias               | Command                                          |
+| ------------------- | ------------------------------------------------ |
+| *rsync-copy*        | `rsync -avz --progress -h`                       |
+| *rsync-move*        | `rsync -avz --progress -h --remove-source-files` |
+| *rsync-update*      | `rsync -avzu --progress -h`                      |
+| *rsync-synchronize* | `rsync -avzu --delete --progress -h`             |