Added missing Yoeman command

Added missing Yoeman command in step 3

Author: SmitaNachan

docs/spfx/extensions/guidance/migrate-from-ecb-to-spfx-extensions.md

@@ -1,7 +1,7 @@
 ---
 title: Tutorial - Migrating from Edit Control Block (ECB) menu item to SharePoint Framework Extension
 description: Migrate from old "classic" customizations to the new model based on SharePoint Framework extensions.
-ms.date: 06/29/2020
+ms.date: 09/03/2020
 ms.prod: sharepoint
 localization_priority: Normal
 ---
@@ -64,6 +64,12 @@ To migrate the previous solution to the SharePoint Framework, see the following
     cd spfx-ecb-extension
     ```
 
+1. Create a new SharePoint Framework solution web part by running the Yeoman SharePoint Generator.
+
+    ```console
+    yo @microsoft/sharepoint
+    ```
+
 1. When prompted, enter the following values (*select the default option for all prompts omitted below*):
 
     - **What is your solution name?**: spfx-ecb-extension
@@ -299,4 +305,4 @@ Enjoy your new custom ECB menu item built by using the SharePoint Framework exte
 
 ## See also
 
-- [Overview of SharePoint Framework extensions](../overview-extensions.md)
+- [Overview of SharePoint Framework extensions](../overview-extensions.md)