Update Readme

Author: dshevtsov

README.md

@@ -1,3 +1,39 @@
 # Page Builder developer documentation
 
-This repo is the future home of all Page Builder developer documentation.
+This project contains the source code of the Page Builder documentation for Adobe Commerce and Magento Open Source developer documentation website.
+
+> **Important update**
+>
+> Adobe Commerce and Magento Open Source 2.4.x documentation has been migrated to Adobe sites. See our new landing pages to access the most current information.
+>
+>[Adobe Commerce Developer Documentation](https://developer.adobe.com/commerce/docs/) (Adobe Developer site)—Develop, customize, integrate, extend, and use advanced capabilities
+>
+>[Adobe Commerce Documentation](https://experienceleague.adobe.com/docs/commerce.html) (Adobe Experience League)—Plan, implement, operate, upgrade, and maintain your Commerce projects
+>
+> Some content was consolidated or moved to different guides. If you have trouble finding a topic, see the [Migrated topics](https://commerce-docs.github.io/devdocs-archive/migrated-topics.html).
+>
+> We welcome contributions to migrated content! You can find similar links to GitHub on the Adobe sites.
+
+## Build the docs
+
+To build this repo locally:
+
+1. Clone the [magento/devdocs](https://github.com/magento/devdocs) repo.
+
+   We use custom automation in the magento/devdocs repo to clone and build MBI docs. This automation will not work if you do not first clone the magento/devdocs repo.
+
+1. Initialize the PB docs repo using rake:
+
+   ```shell
+   rake init
+   ```
+
+1. Build the site:
+
+   ```shell
+   rake preview
+   ```
+
+## Archived docs
+
+To view the archived documentation, see <https://commerce-docs.github.io/devdocs-archive/>.