MC-40719: Product Thumbnails not switching properly for Config product

Author: thiaramus

app/code/Magento/ConfigurableProduct/README.md

@@ -1,5 +1,46 @@
-Magento_ConfigurableProduct module introduces new product type in the Magento application called Configurable Product.
+# Magento_ConfigurableProduct module
+
+The Magento_ConfigurableProduct module introduces new product type in the Magento application called Configurable Product.
 This module is designed to extend existing functionality of Magento_Catalog module by adding new product type.
 
 Configurable Products let the customers select the variant they desire by choosing options.
 For example, store owner sells t-shirts in two colors and three sizes.
+
+## Structure
+
+`ConfigurableProduct/` - the directory that declares ConfigurableProduct metadata used by the module.
+
+For information about a typical file structure of a module in Magento 2, see [Module file structure](https://devdocs.magento.com/guides/v2.4/extension-dev-guide/build/module-file-structure.html#module-file-structure).
+
+## Extensibility
+
+Extension developers can interact with the Magento_ConfigurableProduct module. For more information about the Magento extension mechanism, see [Magento plug-ins](https://devdocs.magento.com/guides/v2.4/extension-dev-guide/plugins.html).
+
+[The Magento dependency injection mechanism](https://devdocs.magento.com/guides/v2.4/extension-dev-guide/depend-inj.html) enables you to override the functionality of the Magento_WebapiAsync module.
+
+## Additional information
+
+### Configurable variables through the theme view.xml
+
+There is a way to configure the mechanism of how images of a gallery should be
+updated when user switches between configurations of a product through modifying the value
+of the `gallery_switch_strategy` variable in the theme view.xml file.
+
+[Learn how to configure variables in view.xml](https://devdocs.magento.com/guides/v2.4/frontend-dev-guide/themes/theme-images.html#view_xml_vars)
+
+There are two available values for the `gallery_switch_strategy` variable:
+
+Value | Description
+--- | ---
+`replace` | In replace mode, images of the parent configurable product will be replaced by the simple product images upon a configuration change
+`prepend` | In prepend mode, the simple product images will be added in front of the parent configurable product upon a configuration change
+
+If the `gallery_switch_strategy` variable is not defined, the default value `replace` will be used.
+
+For example, adding these lines of code to the theme view.xml will set the gallery behavior to `replace` mode. 
+
+```
+<vars module="Magento_ConfigurableProduct">
+    <var name="gallery_switch_strategy">replace</var>
+</vars>
+```