Add XML Docs for WithArgs()

The wording in the XML docs is based on my cursory review of [issue 177](dotnet#177) and [PR 1121](dotnet#1121).

I should add that I only started reviewing Aspire a few hours ago, so apologies if the XML docs aren't accurate - I just figured the best way to get started contributing is to jump right in (CC: @danmoseley).

#Fixes dotnet#1294

Author: ericmutta

src/Aspire.Hosting/Extensions/ContainerResourceBuilderExtensions.cs

@@ -81,6 +81,13 @@ public static IResourceBuilder<T> WithVolumeMount<T>(this IResourceBuilder<T> bu
         return builder.WithAnnotation(annotation);
     }
 
+    /// <summary>
+    /// Adds the arguments to be passed to a container resource when the container is started.
+    /// </summary>
+    /// <typeparam name="T">The resource type.</typeparam>
+    /// <param name="builder">The resource builder.</param>
+    /// <param name="args">The arguments to be passed to the container when it is started.</param>
+    /// <returns>The <see cref="IResourceBuilder{T}"/>.</returns>    
     public static IResourceBuilder<T> WithArgs<T>(this IResourceBuilder<T> builder, params string[] args) where T : IResource
     {
         var annotation = new ExecutableArgsCallbackAnnotation(updatedArgs =>