Start of the UI plugin guide

README.md

@@ -17,6 +17,7 @@
 * [Developer Copr setup for CentOS6](developer_copr_setup_centos6.md)
 * [Internationalization Guidelines](i18n.md)
 * [UI Patterns](ui/patterns.md)
+* [UI Plugins](ui/plugins.md)
 * [Report data API](ui/report_data_api.md)
 * [Shared react component API](ui/register_react_component.md)
 * [Service UI Skinning](/service_ui/skinning.md)

ui/plugins.md

@@ -0,0 +1,30 @@
+### UI Plugins
+
+The UI now supports plugins - rails engines that can be added to the Gemfile, and provide additional menu items and screens for the Classic UI.
+
+For info on how to use a plugin, please see [Plugin development](../developer_setup/plugins.md).
+
+(This section is a stub and will be expanded later. For now, please see (the v2v plugin)[https://github.com/ManageIQ/miq_v2v_ui_plugin] for a working example.)
+
+This is *not* the same as [Simple plugins](simple_plugins.md), which is an older feature using an iframe to point to a specific URL.
+
+---
+
+#### Shared libraries:
+
+Since the plugins' javascript is built together with the rest of ui-classic, it needs to share certain common libraries - this is the list of shared libraries, guaranteed to be available to plugins now (but not in gaprindashvili):
+
+* jquery
+* lodash
+* patternfly-sass (and window-shared dependencies, such as bootstrap-switch, bootstrap-select, etc.)
+* patternfly-react
+
+(For the actual versions, please see our [package.json](https://github.com/ManageIQ/manageiq-ui-classic/blob/master/package.json).)
+
+A plugin is free to add any additional dependencies of course.
+
+
+If a plugin happens to depend on the same library in a different version:
+
+* right now, you can't - either of the 2 versions will get picked, randomly
+* after we update to webpack 5, you shouldn't - this would still mean downloading 2 copies of the library on every page load