nanoc: add README (#7252)

plugins/nanoc/README.md

+# Nanoc plugin
+
+This plugin adds some aliases and autocompletion for common [Nanoc](https://nanoc.ws) commands.
+
+To use it, add `nanoc` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... nanoc)
+```
+
+## Aliases
+
+| Alias | Command               | Description                                        |
+|-------|-----------------------|----------------------------------------------------|
+| n     | `nanoc`               | Main Nanoc command                                 |
+| na    | `nanoc autocompile`   | The autocompile command has been deprecated since Nanoc 3.6. Use [guard-nanoc](https://github.com/nanoc/nanoc/tree/master/guard-nanoc) instead. |
+| nco   | `nanoc compile`       | Compile all items of the current site. |
+| nci   | `nanoc create_item`   | Command was deprecated in Nanoc v.3 and completely removed in v.4 |
+| ncl   | `nanoc create_layout` | Command was deprecated in Nanoc v.3 and completely removed in v.4 |
+| ncs   | `nanoc create_site`   | Create a new site at the given path. The site will use the filesystem data source. |
+| nd    | `nanoc deploy`        | Deploys the compiled site. The compiled site contents in the output directory will be uploaded to the destination, which is specified using the --target option. |
+| nv    | `nanoc view`          | Start the static web server. Unless specified, the web server will run on port 3000 and listen on all IP addresses. |
+| nw    | `nanoc watch`         | The watch command has been deprecated since Nanoc 3.6. Use [guard-nanoc](https://github.com/nanoc/nanoc/tree/master/guard-nanoc) instead. |
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