Added extra clarity for the Getting Started section

Author: protherj

contributing/umbraco-cms/build.md

@@ -17,7 +17,9 @@ If the answer is yes, please read on. Otherwise, make sure to head on over [to t
 
 To run umbraco, we first need to initialize the client git submodule:
 
-* Execute `git submodule update --init` to get the files into Umbraco.Web.UI.Client project
+* Execute `git submodule update --init` to get the files into Umbraco.Web.UI.Client project. 
+  * This can be executed in the root folder of your cloned repository.
+* If you are going to run Umbraco for testing, execute `dotnet run` inside the \src\Umbraco.Web.UI folder. 
 * If you are going to work on the Backoffice, you can either go to the Umbraco.Web.UI.Client folder and check out a new branch or set it up in your IDE, which will allow you to commit to each repository simultaneously:
   * **Rider**: Preferences -> Version Control -> Directory Mappings -> Click the '+' sign
 * If you get a white page delete Umbraco.Cms.StaticAssets\wwwroot\umbraco folder and run `npm ci && npm run build:for:cms` inside Umbraco.Web.UI.Client folder to clear out any leftover files from older versions.