Specify that ContainerRuntimeIdentifier can be plural (#617)

Specify that ContainerRuntimeIdentifier can be be plural

Author: MattKotsenas

docs/ContainerCustomization.md

@@ -41,7 +41,7 @@ which results in a final tag of `8.0-alpine` for a .NET 8-targeting application.
 
 This field is very free-form, and often can be used to select different operating system distributions, default package configurations, or any other 'flavor' of changes to a base image. Consult your base image's documentation for more details.
 
-### ContainerRuntimeIdentifier
+### ContainerRuntimeIdentifier(s)
 
 This property controls the OS and platform used by your container if your [`ContainerBaseImage`](#containerbaseimage) is a 'Manifest List'. Manifest Lists are images that support more than one architecture behind a single, common, name. For example, the `mcr.microsoft.com/dotnet/runtime` image is a manifest list that supports the `linux-x64`, `linux-arm`, `linux-arm64` images.
 
@@ -55,6 +55,14 @@ By default, if your project has a RuntimeIdentifier set, that value will be used
 </PropertyGroup>
 ```
 
+_Set multiple container runtime identifiers for multi-architecture images (tags are `;` delimited):_
+
+```xml
+<PropertyGroup>
+    <ContainerRuntimeIdentifiers>linux-x64;linux-arm64</ContainerRuntimeIdentifiers>
+</PropertyGroup>
+```
+
 > **Note**
 > If you'd like to publish to a musl-based OS like alpine (as opposed to a libc-based OS), you will need to specify the base image _including architecture_, instead of relying on
 > any of the inference described above. For example, a `net7.0`-targeting application that wanted to run on alpine with the x64 architecture would use the `7.0-alpine-amd64` tag of the `mcr.microsoft.com/dotnet/runtime` image (or another base image as appropriate for your project type):