Merge branch 'staging'

Author: VesaJuvonen

docs/spfx/extensions/guidance/using-custom-dialogs-with-spfx.md

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+# Using Custom Dialogs with SharePoint Framework Extensions
+
+Introduction
+
+Dialog is also avaialble for web parts.
+
+> Notice that the SharePoint Framework dialog is currently in preview status and we are looking to collect feedback before it's officially released. Please provide us feedback by using the [sp-dev-docs repository Issue list](https://github.com/SharePoint/sp-dev-docs/issues).
+
+## Setup your Environment
+
+Before you can complete this guide you will need to ensure you have [setup your environment](https://dev.office.com/sharepoint/docs/spfx/set-up-your-development-environment) for development 
+using SharePoint Framework and that you are using latest SharePoint Framework Yeoman templates. 
+
+> You can update your SharePoint Framework Yeoman templates by running following command `npm install -g @microsoft/generator-sharepoint`. 
+
+## Create a New Project
+
+Start by creating a new folder for the project using your console of choice:
+
+```sh
+md dialog-cmd
+```
+
+And enter that folder
+
+```sh
+cd dialog-cmd
+```
+
+The run the Yeoman generator for SharePoint Framework
+
+```sh
+yo @microsoft/sharepoint
+```
+
+When prompted:
+
+* Accept the default value of **dialog-cmd** as your solution name and press **Enter**.
+* Choose **Extension (Preview)** as the client-side component type to be created. 
+* Choose **ListView Command Set (Preview)** as the extension type to be created.
+
+The next set of prompts will ask for specific information about your extension:
+
+* Accept the default value of **DialogDemo** as your extension name and press **Enter**.
+* Accept the default value of **DialogDemo description** as your extension description and press **Enter**.
+
+![Yeoman SharePoint generator prompts to create an extension solution](../../../../images/ext-com-yeoman-prompts.png)
+
+At this point, Yeoman will install the required dependencies and scaffold the solution files along with the **HelloWorld** extension. This might take a few minutes. 
+
+When the scaffold is complete, you should see the following message indicating a successful scaffold:
+
+![SharePoint client-side solution scaffolded successfully](../../../../images/ext-com-yeoman-complete.png)
+
+For information about troubleshooting any errors, see [Known issues](../basics/known-issues).
+
+Once the solution scaffolding is completed, type the following into the console to start Visual Studio Code.
+
+```
+code .