Update landing page with quickstart template commandline

Author: maartenba

src/content/docs/index.mdx

@@ -41,6 +41,8 @@ import Testimonial from "~/components/testimonial.astro";
 
         ```bash title="Terminal"
         dotnet new install Duende.Templates
+        dotnet new duende-is -o DuendeIdentityServer
+        dotnet run --project DuendeIdentityServer
         ```
     </Card>
     <Card title="Demo Server" icon="setting" href="https://demo.duendesoftware.com">