Merge pull request #1436 from itowlson/plugin-authoring-pluginify

Mention pluginify in plugin authoring docs

content/spin/v3/plugin-authoring.md

@@ -134,6 +134,8 @@ $ spin plugin install --file practice.json
 $ spin practice
 ```
 
+> While developing a plugin, you can [use the `pluginify` plugin to automate packaging and installation](https://developer.fermyon.com/hub/preview/plugin_spin_pluginify) for testing in the Spin environment. This saves going through the package-manifest-install cycle every time you want to try an update!
+
 ### Contributing a Plugin
 
 If you think the community would benefit from your newly created plugin, create